** Possible Solution 
**
After comparing differences between 2 PMS setups & getting ready to wipe out my setup and rebuild it, i think, i have found the issue (for me anyway).
After checking the firewall rules many times and deleting/creating rules about a million times i noticed in one screen the rules had changed to BLOCK all incoming connections, including those on the allowed apps.
To quickly check your setup, try the below (windows users)
In the start menu type windows security & open the app
Next click on your active network (it will say active next to it)
Finally check the tick box at the bottom is blank, if it has a tick in it remove it & then retest your PMS, mine returned to normal behaviour straight away.
How or why this changed i haven’t checked yet but just wanted to give you another idea of what to check.
@ChuckPa @BigWheel
Might be worth getting others to check this if they report the same issue.
