I thought I was the only one! I actually discovered this issue when testing the web build for our game and added a setting to workaround it, but I was the only one on the team with the problem. Also, the workaround I implemented wouldn’t be possible for a first person shooter, so I think people with the bug we have are just out of luck :(
The only real discussion I have found of the issue is https://discussions.unity.com/t/webgl-mouse-input-is-just-completely-broken/930168/8. It happens for me across game engines and browsers. It’s so strange.