paulbates

I've recently purchased and installed it on the version prior to 5.8 and it installed as it should and working.
So I'm going literally by the steps you listed, I don't see that you did the install step? That would explain the outcome. Install and reboot
If that's not it, I would go to the pg3x log, set for debug and look at the entries near the bottom for errors related to yolink.

You can do it by storing one of the devices temperature's in a state variable in a program:
If
  Device_Node_Temp not equal State_Var_Temp
Then
  State_Var_Temp = Device_Node_Temp
 
The you can create the program to control the wine cellar by comparing the other device node temperature reading with the variable with the temp variable. There's a tiny arrow head at the end of the line when building the if statement next to the device node you've picked... click it and a list of variables will come up. 
It has to be a state variable for the if statement to function

It should be possible... Use the "schedule" clauses with AND and the other device conditions.
It's hard to be more specific without more info or a sample program you might have started

This is not exactly what you're asking, but there are other ways to debug
Put notifications in key spots in programs to alert you and then remove them once the program is working. I've recently completed several programs and notifications got me around my "bugs"
  As an alternative to notifications, set a variable, If your program is setting variables this is a good method and also recently used this method. To see these changes, open the event viewer (as opposed to the log) and look for entries something like VAR[ 2 7]... where 2 = state variable, and 7= variable number on the list of variables.
   

Looks like you're on an isy 994i. The new insteon i3 devices are not (fully) supported, you'll need a polisy or eisy to fully utilize i3 devices

The combination of older PLM and flaky behavior says it's time to get a new PLM and handle the swap on your terms, not when things get a lot worse and it stops working.
 

Also possible-to-likely is that the new router's ip4 subnet is different than the old router's.
Via the mobile app:
Settings Systems Pick your isy Scroll down to "local connection settings" Your ip and ports will be listed there