When playing Co-op in Mechwarrior 5: Mercenaries, if you get a mission that starts from a dropship (rather than just spawning directly onto the map), you sometimes lose mouse control when it’s time to exit the dropship. You can still fire, and the mouse will work on the game menu, but you can no longer aim using the mouse.
What worked for me
As an Nvidia GPU user, pull up the Ansel overlay using ALT+F2, then close it again. Mouse control returns.
Speculation on root cause
I’ve noticed that when the bug is going to occur, I actually have mouse control while in the dropship itself (and can fire my weapons inside it, which you normally can’t do).
My theory based on that is there’s some kind of issue relating to mouse control being toggled (between on and off) rather than being explicitly set to on or off.
It could also be an issue with Ansel or some other software that might be interfering with what program “owns” the mouse. Since the fix is so easy and has had a 100% rate of success, I haven’t bothered to investigate further, and haven’t even tried disabling the Ansel overlay to see if that’s the issue.
This seems to be an uncommon issue (I couldn’t find anyone else experiencing it specifically in MW5, just in some other games), so if you have it and this helps (or doesn’t help) please take a minute to leave a comment – especially for the latter if you find something that does!