The cause of mouse stuttering when pressing keys has been 100% found

I'll try to be brief🙂

The bug itself is that when quickly pressing certain keys on the keyboard while simultaneously moving the mouse left and right, the image stutters.
However, there's a catch: every time the game is restarted, there seems to be some kind of buffer that fills with the first 4-8 keys pressed on the keyboard.

So, if, for example, I press the W,A,D,C,R,Q,S keys first, there's a 99% chance the bug won't affect them.
However, the keys pressed after this (from about the ninth key and so on) will reproduce the bug.
Moreover, this buffer can "fill" even by clicking the keyboard in the menu. And if the first keys pressed weren't the ones needed for comfortable, dynamic play with parallel mouse movement, then only a reboot and a new input will help.

I tested this theory on almost 100 game restarts.
And now the first thing I do before a game is enter training mode with my mouse, click the necessary W,A,D,C,R,S,Space,Shift and continue playing calmly.
But it shouldn't work like that!🙄

My guide on this topic is on Steam - https://steamcommunity.com/sharedfiles/filedetails/?id=3626300845

UPD: An interesting observation from steam/ZongerX is that when pressing problematic keys, Javelin Anti-Cheat activity increases in Task Manager (in my case, by ~3%).
However, the problem most likely isn't the extra CPU load itself, but rather that the anti-cheat starts some background checks at that moment on those keys that did not end up in the "safe" buffer and those that are not pressed together with "Alt".