So!
We think it seems that all the issues are caused by having the game in full screen mode. We've set it so the game opens windowed, but it won't override a users default if they've already set it to open in full screen.
Could everyone who is still with us, check their linux version and see if there are any issues that are not fixed by taking it out of full screen mode and into windowed?
Thank you all so much. We're not sure what's causing the issue in fullscreen mode, but this would at least let us know that all the users can use the game.