Geddy

The move from 4.x to 5.x was a big step so any move to 5.x to be able to use UD Mobile will require some time to get things sorted out.
There have been a lot of posts about this, but simply saying...read the 5.3.4 release thread. Skim it and look for pitfalls. 
The simple answer to your question:  Go directly to 5.3.4. Do NOT think about anything else. You don't have Z-wave so you don't need to worry about the warnings on 5.0.16C. Don't even consider installing some random version of 5.x and then thinking you will upgrade to 5.3.4 if it went better than expected. The best, and perhaps safest thing is to bite the bullet and install 5.3.4.
Now, here are some pitfalls to watch and hopefully minimize your "pain" (interaction) in the update process.
Backup current system - yes, it tells you to do this in the release thread, but do it again just to make sure you've done it.
  On the ROOT folder of the Programs tab right click and select "Copy to Clipboard" (it's the LAST option in the menu).  Paste the programs into a (plain) text editor (like NOTEPAD for Windows). DO NOT PASTE IT INTO WORD OR OTHER WORD PROCESSING PROGRAM - it could auto format text and you don't want that.  MAKE NOTE of any "Disabled" programs - on some occasions when you go to 5.x all programs become enabled so you will need to disable any permanently disabled programs you have.  If you have any "adjust scene" programs you will need to correct those once you update. 
  Be sure when you're done that you properly clear your Java cache (checking all three boxes in the process!)

  Download a fresh start.jnlp file from UD website or the wiki site. (I usually tell people before doing this to delete any OLD start.jnlp/admin.jnlp files from anywhere on the computer as sometimes OLD files will be used, and you need a fresh file that you just now download.   
This should get you there. Give yourself some time to accomplish this. Don't expect to have it done in 5 minutes, but it usually shouldn't take too long either. 
Hopefully you're currently running 4.9 (last 4.x version released). If you run into issues you can download 4.9 again from the previous release area and restore your 4.9 backup and be up and running quickly. 
Post back and let us know how it goes. 

I experienced a similar situation trying to update the Polisy. 
Take a look at this solution posted by @Michel Kohanim to help. Step #2 helped resolve my issue.
 

@elite-rob If Insteon switches it's possible they got locally linked and the ISY (994?) would not notice/recognize that link in the admin console. You can fix this several ways, but I think the easiest is to:
Factory reset the switch. Then re-link to ISY. 
I think there might be a way to make this work without removing it from the ISY tree and right click on the device and "restore device" and it should write back everything the ISY has for that switch. I've never personally tried it this way, but saw an old post referencing this method. 
 
Note - It's often suggested when installing switches to always perform a factory reset before linking to the ISY. This clears out any existing links or strange QA codes that might have been introduced to the device from the factory. 
When linking to the ISY there's always the option to "remove existing links". This way sometimes help stops this from happening, but is not always 100% accurate. That's why some will always suggest a factory reset just to completely clear any existing internal memory. 
Google search for the type of switch you have to get the proper process for factory reset.
 

Not having this issue.
Doubtful that it's the whole issue, but you need to update your Java. Current version from java.com is Version 8 Update 351.
Delete previous copies of start.jnlp or admin.jnlp (be sure to look for multiple copies of same file i.e. start (1).jnlp)
After you do that:
clear your java cache, (Be sure you check/select all 3 boxes in this process!) download a new start.jnlp file from the Universal Devices site or through the Wiki. Once you are able to log into admin console confirm your Firmware and UI match (Help -> About). They should match EXACTLY (even the date/time code).
 
Other items to check:
Is there a steady bright blue light on the front of the ISY (if not see here).
  Do you see the ISY as a connected device if you log into your Router?  Can you ping the ISY from your computer? 
  You say UD Mobile works "most" of the time. Is that accurate or assumption? If really is "most" of the time it sounds like a network issue.
  Log into my.isy.io and check the error log (Tools -> Select Tool -> Logs) to see if there are any significant errors seen. Check error codes in this wiki article  
Let us know how things look once you check/fix/update the above.
 
 
 

At this point I'd say don't worry about Polisy. Take a look at the next gen eisy.
But if you want to learn more about Polisy:
https://www.universal-devices.com/product/polisy-pro/
https://wiki.universal-devices.com/index.php?title=Polisy:User_Guide
Polisy and Polisy Pro are out of stock.  So can't get them currently.
 

Quickest and easiest…. ISY Portal account…
https://wiki.universal-devices.com/index.php?title=ISY_Portal_Admin_Console
 
Plus, MobiLinc works with ISY Portal for remote access…
https://wiki.universal-devices.com/index.php?title=ISY_Portal_MobiLinc_Configuration
 
And to fix your default email issue you need to update to 4.9 if you’re running 4.x firmware. Otherwise setup a Google account and use that.  Directions also in the wiki.
 
Finally….read the information in current release area (on the forums) for ISY Launcher for current/best way to access ISY locally (the “old” method of a browser and Java don’t work so need to learn the new way). It’s simple if you’re as tech savvy as you say you are.   
 

@fbelg210 follow the instructions here:

 

@FerventGeek not sure about that cable you link to, but know this has been covered before (when lots were migrating over to Polisy). 
I think there's something with only having a few wires connected on the serial side so not to cause issues. I am not in the know of what is/isn't good to connect. 
I just know there were a lot of links to this product at Amazon (thank you @MrBill) 
This post from @Brian H should be able to tell you something about what wires to connect up (pin-out). 

For Gmail you should setup this way:

I just set this up on my Polisy and it worked perfectly. 
Take a screen shot of what you have setup and post it (blur/remove any personal identifying information)
The biggest issue is the "From" needs to be in the format (if you use a name) to have the colon (:) between the name and email address. I also use Gmail and 2FA and have ISY app specific password setup and this works. I just changed from the default for Polisy to this and it sent a test message without issue. 
 
What does this mean? Are you using the ISY "Use Default" settings and you got an error?
Make sure you have entries in the "Groups" to send the test to. If that's blank it might give you errors because there's no outbound recipient. That would give you a different error though so doubt this is the problem. 
 

Read the Wiki and other posts here. Gmail still works perfectly. You just have to follow the directions to set it up.  
 
https://wiki.universal-devices.com/index.php?title=ISY994:Configure_Mail_Server_Settings#Configuring_gmail_Account
 

Must have missed it when you read the area about how old it is.
https://wiki.universal-devices.com/index.php?title=Polisy:User_Guide#Polisy_OS_Versions_Below_13
(It is a little hidden between text. Wiki formatting doesn't allow/like to have a lot of bold and different text colors so can't make it "pretty" to really stand out.)
The command is:   sudo uname -a
 
No worries. We all do it and we're here to help.

The orange arrow is for a flash chip to repair an issue that happened during one of the early update phases. It's only meant to be in there temporarily. I think it was only limited to that short period of time that an update corrupted a chip in a small number of original builds. 
While I doubt there is much difference, if it's something you're worried about please open a support ticket to ask the question directly with UDI. 
Submit a Ticket:       https://www.universal-devices.com/my-tickets
 

@someguy PG3 current version is 3.1.12 - release announcement here:
 
What Techman gave you is Firmware for ISY on Polisy. 
You can find all current release information here - https://forum.universal-devices.com/forum/339-current-release-announcements/
 

@adam48 The 60006 and 140000 errors mean the device is not able to connect to the internet. Either you didn't put the network cable into the correct port or it's not being assigned an IP by your router.
What is the light pattern on the front when you boot it up? 
I looked further down your log and see the 110022 and 110012 errors. Those indicate SD card issues. Either the SD card is corrupt or just needs to be reseated after you opened the ISY to remove the z-wave card. 
Also, you don't have to clear java cache each time you try to connect. As long as you're using the ISY (IoX) Launcher method to connect to the admin console. You should only have to clear java cache if you're having other issues or have upgraded firmware. Often times when Java updates though the icon on the desktop will go away and you would need to clear the Java cache then and download a new start.jnlp to get the IoX Launcher icon again.
 
Wiki links for your issues:
Error codes - https://wiki.universal-devices.com/index.php?title=ISY-99i/ISY-26_INSTEON:Errors_And_Error_Messages
Light patterns - https://wiki.universal-devices.com/index.php?title=Main_Page#Front_Panel_LEDs/Lights
 
It's possible that your time issue was because the ISY didn't have internet connection. You probably could have left the z-wave card in there first. I might put it back in, reseat the SD card. Plug everything back up. Plug the PLM in first. Wait a few seconds. Power up the ISY, and watch the lights on the front. 
Once you have internet restored to the ISY everything should work correctly again. 
Strange that this worked. Perhaps it wasn't long time of internet outage, but you clearly were getting errors relating to lack of internet connectivity.
 

@jlegault That's an issue you'd have better luck with asking in a Java forum.
Perhaps this will help: https://blogs.oracle.com/javamagazine/post/java-on-arm-processors-understanding-aarch64-vs-x86
Or this - https://macperformanceguide.com/blog/2021/20211216_1200-Java-for-M1-Macs.html
The issue might be that admin console is developed for standard Java that is available just by going to www.java.com and clicking download. I'm assuming that macOS still does this like Windows computers do.
Users have reported errors when using multiple versions of Java or versions that are intended for different applications. 
If getting Java from java.com is not "native" then I'd say the answer is no. 
 

Yes, you would be nuts! This should not be something you attempt.
As @stillwater points out you cannot run 2 PLM for only Insteon devices. Now, if you wanted to run two different systems you could, but Insteon can only be controlled by one (1) PLM at a time. Others here have had Insteon on the existing ISY+PLM and run different systems on Polisy and IoP. I don't entirely know the setup for if you get into node servers of how to point some at the ISY and some at IoP. So, really, you'll end up making it harder on yourself. If you attempt to have some items moved over to IoP you run a big risk of having 2 PLM sending powerline signals and creating noise and disrupting the path from one controller to device. So I wouldn't even suggest having a sub-set for testing. 
Make sure you follow the steps in the Polisy User Guide in the wiki for migrating from ISY994 to IoP (ISY on Polisy). 
Many have completed the migration over the last several months. While some processes might have altered slightly you should read through this thread to know about any "gotcha" moments that might get you.
Remember...lots of user-to-user help here if you run into issues. Good luck!
 

Are you sending texts from an email? This has been asked/answered in many posts on here. The "old" method of sending texts to a #@vzw<whatever-email> is very low priority for most carriers these days. The suggested route is to use network resources, node server, and/or UD Mobile alerts. 
Run a Google Site Search for slow texts and see what has been said.
It's not just you, and it's not UDI. It's the cell carriers. 

@Dean  It's not an "internal" port forward. It's actually suggesting that you port forward on your router/firewall to be able to receive external connection from the Rachio server. 
https://github.com/UniversalDevicesInc-PG3/udi-rachio-poly/blob/master/README.md
 
Under the heading "Polyglot Custom Configuration Parameters"
 
Also note in the install instructions this comment:
My guess is that's so the DDNS would update if your external IP should ever change you won't have to fix the node server settings.
 
I'm not a user of this node server. Just happened to see these parts in the readme files and wanted to point them out.
 

@heitjer are you using the IoX launcher (Formerly ISY Launcher) method to access admin console? You mention you’re accessing through some Insteon.jar access. Not sure of that process….really must be an old process. Please read the current release area for the ISY Launcher method discussion   
It sounds like your Firmware and UI don’t match. 
 
When you reset the ISY you get a basic Firmware that you then need to manually upgrade to a full hardware (found in current release area).  
 
Specifically follow the steps here - https://wiki.universal-devices.com/index.php?title=ISY-99i/ISY-26_INSTEON:Replacing/Formatting_an_SD_Card
 

@KTrautman Not sure if this is the same problem macOS has caused in the past or not, but take a look at this thread solution to see if it resolves your issue:
 

@johnjces I believe if you're in the admin console and you rename the ISY in the tree it will then push that name to the Finder.

Just right click on the ISY name and "Rename" is an option. Close admin console and re-launch IoX (ISY) Launcher and it should display the new name.
 

You cannot. That's currently not supported. The only way you could do this would be to run a VPN at home and connect via VPN while remote and then access it. I'm sure there might be a way through port forwarding, but it's not secure in anyway so I wouldn't suggest doing that.
Only ISY on Polisy can be accessed remotely on the Polisy. PG2 and PG3 all have to be accessed and managed locally. 
 

There are some old videos showing the install. I know there were some topics earlier this year saying that something in a current/recent release for RPi changed the process. Having never attempted such an install I can't tell you what to watch for.
Check the PG2 area of the forums.
Here's the GitHub for PG2 - https://github.com/UniversalDevicesInc/polyglot-v2
Videos - https://forum.universal-devices.com/forum/158-instruction-videos/
 
Found those posts from earlier this year that might help:
 
 
 
Good luck. Know that PG2 is no longer being developed so support could be limited. 
 
 

@TVC15 There have been a lot of posts about this through the years.
Info about the power supply can be found in the wiki - https://wiki.universal-devices.com/index.php?title=Main_Page#Front_Panel_LEDs/Lights
 
Quick search of the forums found this topic:
 

@DJonas how old is the ISY994? Have you ever had power supply issues? What's the light pattern on the front of the ISY? And if you're willing to power cycle it again watch the light pattern when it starts up. 
https://wiki.universal-devices.com/index.php?title=Main_Page#Front_Panel_LEDs/Lights
Since dashboard loads it seems to be getting to the device on the network. 
Leads me to think it's computer related or else power related and the draw on power to load the admin console might be causing the issue. 
Before trying anything else post a screenshot of what you see when you load admin.jnlp admin console. You say above it shows ISY information, but nothing is selectable. Feel free to blur out personal info. 
Also, be sure you check Firmware and UI in the Help -> About menu (is that even selectable?
Next steps I would suggest are:
Clear Java Cache (yes, again). Be sure you select all three boxes in the process
Refer to this wiki article to remove .state files - https://wiki.universal-devices.com/index.php?title=Main_Page#Admin_Console_Minimized/Invisible_and_Cannot_be_Restored   
(***NEW STEP you might not have done before!***) Delete ALL start.jnlp or admin.jnlp files downloaded ANYWHERE on your computer download a fresh start.jnlp version from UDI - https://isy.universal-devices.com/start.jnlp Run start.jnlp Should put fresh ISY Launcher icon on desktop
Run Launcher - Try Admin Console (Cloud)  
 
Make sure when you run ISY Launcher that it opens the "ISY Finder" window that looks similar to this:

 
Report back with what happens.