Valve hasn't fixed the issue where your mouse on menu and ingame is broken and u have to restart the game.

Never seen this mentioned here yet but ppl experience it all the time, it happens often if u change your resolution. Then when u try to move/click on an icon in the menu, the cursor registers in another area. Then when u try to aim in game, ur sens is slower or it doesn't move in certain parts, making it hard to look up and down.

Restarting ur game fixes it but sometimes launching the game it has this issue off the bat, so u just have to restart again. Its been like this for many months, maybe since the game came out lol.