There's no obvious reason for it messing up in game. Holding a button should hold. if it doesn't, either the mouse is glitching or another app is intercepting the inputs.

Check your windows settings. Keyboard settings like sticky keys and all that stuff should be disabled as a matter of course. Windows mouse settings has a click lock that may be messing things up, so make sure that's disabled. There may also be a click assist which turns mouse inputs into an autoclick.

If verifying files doesn't work, you'll have to dig deeper and into stranger places to find the problem.