Not really issues. More like configuration fun!
Anyway Win10 Pro 21H1 (Os Build 19043.1826)
Multiplicity is Version 3.57 Build 00103 on both machines. Although the Primary says 000103.km
WindowFX is Version 6.12
I only thought WindowFX because it has the functionality to make non-active windows semi-transparent, but now you mention Multiplicity then that makes more sense. Basically when you leave a PC to move to another then the current active window on the first PC should become inactive. I mean the whole PC is then effectively inactive as you have moved onto the other PC. In my example this would make WindowFX turn the window semi-transparent.
It's similar to another report I made for Multiplicity where the mouse cursor should disappear from the PC you are leaving, esp if the PC is just an information PC (like mine is for news, meetings, music etc).