shortcut-F12 not opening the GSX menu randomly
F12 was never supposed to open GSX. Ctrl+Shift+F12 does. So, if you really used to have just F12, it's because you changed it, and using just F12 make it easier to run into conflicts, especially with non flightsim-related software.
Now, addons using only the proper SDK way to detect keystrokes, shouldn't be cause issues and should work if one use F12, another one Shift-F12 and GSX Ctrl+Shift+F12 but, there are addons that reads the keyboard in a different way, so they might have stolen the whole F12 key, with all its combinations of shift keys.
The only addon I recently added is UTLive: not sure it shares any key with GSK, have to check better.
I think it does, since it use some of the the F12 key combinations to change the traffic complexity.