Why does my mouse/cursor speed up in game?

Who else has this problem?

Sometimes, I think it even slows down?

Did you check if your system has “mouse acceleration” checked on its options?

That’s not it. This is the only game where this happens.

Also, it happens randomly, in game. For example, it will speed up 20% 5 minutes into the game.

single or multiplayer?
if multi, then its connection being rocky

Check your in-game resolution.
Maybe you have a 4k monitor but it’s HD in-game. Then your mouse can speed up.

could be. my ISP is giving me sh*t

I don’t know how to check that. 4K v. HD is not an option in graphics settings, as far as I can tell. My system passes the benchmark test. Still, I don’t think that’s the problem. The problem only started a month or two ago, and I’ve been playing for several years.