The Hotkey I have setup is one key for Primary and one key for Secondary. So when I hit the hotkey for Primary it will go to the Primary screen and when I hit the key for Secondary it will go to the Secondary screen. The Hotkeys only work on the Secondary screen in Full Screen mode of games. If I am on the Primary Screen and in Full Screen mode of a Game I am playing, and I want to switch to the Secondary screen via the Hotkey it doesn't work. I have to Alt-Tab out of the game then the hotkey for the Secondary screen will work from the Primary screen. Now if I play the game on the Secondary Screen (Secondary PC) even when in full screen mode the Hotkey works fine, I am able to switch from Secondary to Primary by Hotkey when the game is in Full Screen. I don't know why the Hotkeys will not work on the Primary when a game is in Full Screen mode.
I tried full screen mode in Chrome and it works fine, so this seems to be game related, but just don't understand why it works on the other PC but not the main one.
OK I did some more testing. I swapped Primary and Secondary in the Multiplicity App, and the problem follows what ever computer is set to Primary in the app. So the issue is related to the APP itself and witch ever PC is set to Primary, so its not related to any one of the PC, both my PC's are confirmed to work just fine with Hot Keys when Games are in Full screen mode when either one is set as the Secondary but not the Primary.
Here are some pictures from my configuration.