Geddy

@Papa C Are you only asking for how to access IoP while remote?
If you are trying this while remote then no. This will not work.
You will need to use the Admin Console that is available in the ISY Portal -> Select Tool -> Information -> ISY Information screen.

 
One note about this...I've had issues with the finder keeping the URL stored (from remote computers). Sometimes it will be there and other times it's just gone. So I always save the finder addresses (as long as the computer you're working on is yours) then you can load that file and not have to go through the ISY Portal to get (copy/paste) the URL again. 
If you're on a laptop that you are using to access AC locally and remotely (at different times) then it will be two different entries. Perhaps you could use the one ISY Portal login for both and it might not get confused, but I've never actually tried that. You can add both and save that file then load it and both should appear if you need to load the finder file.
 

More than likely you don't yet have PG3 running. How old is your Polisy?
Please see the Polisy User Guide in the UD Wiki for further information of getting PG3 installed/running.
As @MrBill suggests if you're just using the IP address with no port (:3000) given then you're accessing the PG2 interface. 
If your Polisy is "older" or hasn't been updated you need to follow the steps in the Polisy User Guide to get get PG3 (if you're not version 13). You'll need to connect to the Polisy via SSH. Details are all in the wiki.
PG2 display when accessing the Polisy via basic IP address:

 
PG3 display when accessing the Polisy via ip_address:3000:

 
Once you have PG3 installed you should see this when you run the ISY Launcher:

 

Make sure you get the ISY Cookbook. It will have lots of programming information that should help. 
 
1)  programs are event based and “run” when the “IF” statement is true. So if you have a program that says to do something at 7pm and have it set for every day then it will “run” the “THEN” line at 7pm. 

2) yes, I think. But basically if you have a generic program to turn something off at a time it will turn off then   If that time is 1hr after the program turned it on then it will go off. Again, read the cookbook for programming education. There are also some good videos on YouTube to help you learn.
3) the else is used in the false of the IF.
basic (because I’m on a tablet rather than a computer)
if from sunset to sunrise
then turn light on
else turn light off
 
This would turn the light on at sunset and turn it off at sunset. Once you learn the programming skills this will be clear. 

Please start with simple timer programs then work up to more advanced and elaborate programs so you understand what you’re doing.  
 
Welcome to the forums and have fun learning ISY/Polisy. 
 
 

Not where it's coming from..at least not outside the ISY. If you see traffic in it then it is traffic within the ISY, but it won't tell you if it's being triggered by something outside the ISY (at least I don't think so...)
I just tested by turning a light on/off via HomeAssistant and directly in the admin console. They are identical events thrown. So, there's no way to tell where it came from, but that something was sending traffic to/through the ISY.
And you're 100% certain you don't have any programs in the ISY that could trigger such light status? Check the summary tab of the program area and see if any programs have run recently (or around the 9:00 time.). You can SORT the last run time by clicking on the column header. 
Only other thought would be to disconnect devices just before 9pm and see if it does it. Might take a couple of days if you disconnect one-by-one to figure out what's doing it. 

Thanks to a little help from @bpwwer the trick is the IP has to be formatted in an "odd" way that I wasn't expecting. I fixed in my PG2 node server setup and then added in PG3 and it worked right away. So, I think it should also work in PG3, but check and confirm if you don't mind.
Key = bridges
Value = ["#.#.#.#"]        (MUST have the square bracket AND the quotes)
In PG2 see below:

 
As soon as I set that and restarted the node server it told me to press the button on the hue. After doing that nodes filled in right away!
 

Welcome back to the forums. Good luck with what you want to attempt. Just to be sure...make sure you do have an ISY994 and not a very old ISY99i. 
When was the last time you attempted to access the ISY994? Were you able to get admin console to load?
If you can open admin console please go to "Help" -> "About" and post your screen shot of the firmware and user interface you are using. 
If you cannot (or have not) access admin console recently note:
ISY Launcher - a new process for accessing the ISY Admin Console; released in 2018 in this post: https://forum.universal-devices.com/topic/24381-isy-launcher/#comments
This method does not require a web browser to remain open as the old (now, very old) process used to. Since most browsers don't directly allow that java process to run.
Firmware - If you are on Firmware 4.x then you can use the auto update process to get up to 4.9. This is the last version in the 4.x branch and the auto update to this level does not require much involvement. Release notes about changes in 4.9 are found here: https://forum.universal-devices.com/topic/31907-release-49-isy994-last-release-on-4x-branch/
 
 
Update - If you're feeling more adventuresome and wanted to venture into the 5.x world then get ready for some work. It's quite a process and requires that you follow the steps very closely. Make sure you read all the update process steps before attempting so you know what to expect! Since you say you have "simple" programs that are mostly just timers you might not have much to adjust, but if you use scenes and "adjust scenes" in programs then you will have more to adjust. 
Current release for 5.x branch is 5.3.4 and can be found here - https://forum.universal-devices.com/topic/33287-534-update-for-isy994-july-30-2021/
 
 
Ultimately, it's up to you to determine if you're good with how it's running just to make your minor adjustments and let it keep rocking & rolling. Otherwise, you can update to the version you're most comfortable with. I might suggest just going to 4.9 if you're already at 4.x just for some slight bug fixes and modifications through the years. Since you don't have a current need for node servers and aren't running a new Polisy then 5.x isn't really necessary. 
 
Finally, for review and tips and other help please review the ISY Wiki - https://wiki.universal-devices.com/index.php?title=Main_Page
 
Let us know what firmware you're currently running and be sure you confirm you've got an ISY994
 

@Chris McKean It's possible that your password for the setup for the IoP is not correct and it's not able to make the connection to the IoP process. If you edit the IoP do you see the eye/show icon (seen in the link posted above). Review your password to IoP to confirm it's what you use when you open admin console for IoP. 
I'm not much help with reading logs, but review the main logs for PG3 and see if there are some errors trying to connect to IoP.
Perhaps @bpwwer can help with an idea of what to look for if Polyglot is not able to sign into the IoP to setup the nodes.
If nothing is being sent to the IoP then last attempt would be to remove the current IoP settings and set it up again. Being sure to add user/pass for the IoP specifcially. You'll get a warning that things will be removed. So if you've setup IoP make sure you make a backup so you can restore if you remove the IoP.
Currently there several different areas you need to enter passwords and each one might be different. 
 

The app specific password is not like the standard 2FA as you say needing to refresh if IP changes (or other factors change). I've had a spare Gmail account setup with the security settings since they were available (probably before 2016) so I've always used the more secure method. I've never had to change/update my Gmail settings. However, I do just because I think it's smart to change/update passwords (even system generated long (16 digit) passwords). But, if you didn't change it yourself then there's no need to change it. It just works. That is until Google changes their methods again.
It's possible that you have advanced security on already, but the old way still worked until the end of May. I simply picked the Elk post because I remember it recently. 
There's also an area in the Wiki that has always described the "optional" method for setting up Gmail. That's just the required method at this point. 
This can be found in the wiki- https://wiki.universal-devices.com/index.php?title=ISY994:Configure_Mail_Server_Settings#Configuring_gmail_Account
 
Yeah, I know Yahoo! changed their process a while back as well so I guess it would be only a matter of time before Outlook does the same thing. 

@landolfi admin console isn't intended to be left open 24/7. What's your reason for leaving it open for so long?
The main function of admin console is simply to setup the ISY function. Once setup things should just work. And therefore no other user intervention through AC would be required.
If you're looking for a different option then I would suggest getting UD Mobile and running on a mobile device. Still not expected to be kept "awake"/active 24/7, but seems to be much better for being left running in the background (at least on my iPhone) and opening and connecting on demand if/as needed. 
But again, the whole part of automation is not to require user intervention. There have been lots of reports (as I recall...several years ago) of issues similar to what you experience. It's a nature of the beast of Windows+Java. It's not meant to be constantly running. So what you are experiencing is "normal". Just close AC after each need and launch again when needed again. 

@Bumbershoot Same issue...I expect. 
 

@Bumbershoot My guess is you must have run a random update recently. 
Please see this topic for information that might help:
 

So you changed the actual content in the custom notification? If you go to the Configuration -> Emails/Notifications -> Customizations tab then click on the area for "Customized Content" it should open up the actual message that it is sending. Make sure you fixed the typo in there. Either the notification didn't change if you had it specific to a device rather than a node variable.
It appears that your typo is in the email account setup itself.  It's showing a from "Spriniler System". That is more than likely an email system issue. 
What is shown in your "SMTP Settings" area? 
 

UD Mobile is for ISY 5.0.16 and above.  (Currently for ISY994 devices without z-wave I would suggest 5.3.4)
Learn more about UD Mobile in the UD Wiki.
I have about as many devices as you do, but they're all 2015 and newer (roughly). Thankfully I haven't had the same fail rate that you're experiencing so perhaps your units are much older or you have power supply issues. Either way, you might want to see if you've got a home electrical problem rather than an Insteon problem just to be sure something isn't frying those devices. You wouldn't want to switch to a different type of device and still have the same fail rate.
Since you're only Insteon (and few x10) then I'd say your upgrade to 5.3.4 should be mostly smooth. The only major issue going from 4.9 to 5.3.4 is if you have programs that use adjust scene. This is because of the change of how scenes are handled in 5.x.
The key (tip/trick) is to copy all programs to a text editor so you can refer back them after the upgrade and adjust accordingly. Never expect to adjust (or recreate) programs from memory. 
In the program tab of the admin console right click the root "My Programs" folder (of if you changed the name whatever the root folder is). Then select Copy Folder to Clipboard (note...last option in screenshot below). Now, paste that to a text editor (in Windows I suggest Notepad - just something that will NOT auto format any text). Make sure you do not stop at the option to "export to clipboard". That will give you an xml file and be more difficult to read. The text pasted from the "Copy Folder to Clipboard" option is clean and clear to follow for reference.

What you will get in Notepad will start like this: (very easy to read programs this way)
=================================================================================== My Programs - [ID 0001][Parent 0000] Folder Conditions for 'My Programs' If - No Conditions - (To add one, press 'Schedule' or 'Condition') Then Allow the programs in this folder to run. Another note to keep up with...make note of any disabled programs you might have. When I upgrade from 4.9 to 5.3.x all my disabled programs became enabled and I had to turn them off again. Some around here will mark disabled programs by name or put them in a folder called disabled.  Disabled programs will show up in your text file with [Not Enabled] clearly shown.
Now is also a good time to go through and possibly rename programs so that ones that run processes in the same room or rely on other programs might be close together in the name list for ease of reference.
It's been almost a year since I upgraded, but still remember that it took me less than an hour to make the upgrade and confirm/adjust programs. Then, over the following weekend if I noticed programs not doing what I expected just spent a little time fixing those up. There weren't many, but there were a few minor tweaks to make.
 
Once up and running with 5.3.4 then you can begin using UD Mobile. It's really becoming a great addition to the ISY world and becoming quite powerful with options. 
Final tip - BACKUP! BACKUP! BACKUP! Make sure you backup your current setup before you attempt the upgrade. Since it's a manual upgrade that's a step in the process, but it's good to run one before attempting the manual upgrade too.
Then, when you get to step 7 in the process just do the first part:
This will download/add the ISY Launcher process for accessing Admin Console. (If you're on Windows this is a simple process...on Mac it's a mixed bag) Run the "start.jnlp" once and it will install the ISY Launcher icon to your desktop. Now, always use this to access the admin console. This will usually open the "ISY Finder" window and should automatically list the local ISY (as long as it is found on the local network). 

 
If after you go through the upgrade process and have issues jump back here and let us know what issues you're having and somebody might be able to help. Otherwise, open a support ticket with Universal Devices (https://www.universal-devices.com/my-tickets/) for individual support for your issue.
Good luck! 

@Bob Amott welcome to the forums. Sorry you're having difficulty. Sadly, I do not use macOS so can't help very much other than try to point you in some generic directions. Do you happen to have a Windows computer you could try this on? There have been some mac users that sail through without issues and others that something in the system just blocks everything they try. 
But for starters make sure you check out the wiki for Mac user troubleshooting:
https://wiki.universal-devices.com/index.php?title=Main_Page#MAC_OSX
and here:   https://wiki.universal-devices.com/index.php?title=Main_Page#MAC_Users
 
Are you going to continue to use the 994i or are you attempting to setup ISY on Polisy (IoP)? Indeed if you're going to migrate to IoP then you will need to update the 994i to 5.3.4 before you can then attempt to migrate to IoP. 
 
The firmware for the 994i is looking for a .zip file. I'm not sure if the macOS is saving the .zip file to what you're saying is .img file type, but this is the first issue. The file downloaded should remain a .zip (compressed) file. Do not unzip/decompress it. 
 
Finally, and as much as I hate to say this...probably best to open a ticket and get Universal Support to walk you through specific steps for macOS for full upgrade. Upgrading from 4.x to 5.x is very complicated and if something isn't right there's a lot that can go wrong trying to help through forum posts. So hopefully support is better able to handle live help and support on macOS.
 
 

I agree with @DennisC, you should upgrade to 5.3.4. It's the most recent supported firmware for ISY994i. While there might be very few changes from 5.3.3 to 5.3.4 it's enough that it would be the first step in further troubleshooting any other issues you have.
As do your exact experience - your brother has the "Launcher" which loads the finder and allows the computer to download the UI to properly match the firmware with every launch. (Thus, "Launcher")
You downloaded the admin console for the direct version you installed. It would be just as though you downloaded admin.jnlp from the ISY994i directly. 
These two routes to access the Admin Console act differently, but they are in fact the same once you access the ISY994i. 
Since the Launcher was introduced in 2018 that is the most often suggested and the recommended process for accessing the ISY994i admin console. It was designed with 5.x in mind as beta builds were being released so users would always have firmware/user interface matching. 
So nothing is "wrong" in your setup.  You're just taking different routes to get to the same destination. There have been a lot of reports of the font/display to be different as we moved into 5.x. You can change those settings, but odds are they won't stay for long as they tend to be dropped and need to be reset.
But, be sure to go ahead and upgrade to 5.3.4 (since you're so close it should be very quick and not require any additional effort, but be sure to follow the steps as outlined on the release post.