Mouse rotation control locks in 1st/3rd-person games

System Information

• GPU: GTX 1060 6GB
• Driver/LLVM version: 4.6.0 NVIDIA 430.34
• Kernel version: 5.0.0-21-generic
• Link to full system information report as Gist:
• Proton version: 4.2-9

I confirm:

• that I haven't found an existing compatibility report for this error.
• that I have checked whether there are updates for my system available.

Symptoms

I've encountered a bug in certain 1st/3rd person games where instead of being able to rotate around 360 degrees and beyond like normal, the camera gets locked to a 90-degree area and I'm unable to rotate the camera beyond that area. Fortunately, it can be fixed by alt-tabbing or pressing the super key, but I shouldn't have to do that.

Out of all the games I've tested [Oblivion (22330), Empyrion (383120), Subnautica (264710) (experimental branch), Fable Anniversary (288470), DOOM (379720) and Warframe (230410)], it has occurred in Empyrion, Subnautica and Warframe, although I am still in the process of testing Oblivion and Fable Anniversary. I obviously believe this to be a Proton problem since it isn't unique to one game.

Reproduction

Unknown. It happens at random; there's no one scene in any of these games where it only appears.

The report names no source file, test, or reproducible entry point. Start by reviewing the reported behavior across Empyrion, Subnautica, and Warframe and reproduce it with the supplied Proton and system details; done means identifying a consistent trigger and a verified fix or focused diagnostic evidence.