Could you try going on official server for a bit and see if the problem is present there?

Did you try “verify file integrity” of the game?

Did this problem start suddenly or maybe some software/hardware change has happened?

Could be a bug but…
A VERY viable option: your mouse is “near end of life”. I have see several… rodents… start misbehaving under certain conditions, before slowly shutting down overall (left button obviously being most used)

EDIT: small typo