Bug #1 - ADS Bug (or at least one variant of it) - Character begins raising weapon, then lowers it automatically, pressing RMB after this results in no action, however the next time you press RMB after that, the weapon will raise again as intended.
Method of reproducing the bug pretty consistently -
Hold W, A or D
Tap RMB to toggle ADS
Tap C to crouch (Almost immediately after tapping RMB, just as the gun is starting to raise)
Seems to help if character is on an incline (see additional information section)
If done correctly, the character should be crouched and the weapon seen briefly raising and then lowering automatically, if you now try to press RMB to raise weapon, nothing will happen - the next time you try to click after that it will work.
Sometimes after you enter the bugged state, you will notice that tapping C to stand up again can cause the character to automatically enter ADS - this seems to suggest the character is technically in ADS the entire time(?) but you cannot see it when you crouch initially. (You can see this at 1:06 in the first video - my only input there is C to stand)
This would explain why the second press of RMB does nothing, as the character seems to be lowering the weapon in the background without any animation present.
Just for clarity - the times in the video where I do ADS properly is because I messed up the timing and the game works as intended, the times where it looks like I simply crouch is when the bug is happening, where it should've put me into ADS but doesn't.
Bug #2 - Movement bug that occurs when character is in 'ADS bugged state'
After you've entered the bugged state, if you try to crouch-sprint you'll notice the character cannot move properly and will be sprinting on the spot/rubberbanding, you can then transition into a standing sprint and the bug will continue.
This only happens if you DON'T press RMB at all after becoming bugged - I assume the game thinks you're trying to sprint while the character is in ADS, which should not be possible, so fuckery occurs.
If you do tap RMB once after becoming bugged (the tap where nothing seems to happen) then character movement works as intended.
Bug #3 - Ghost Bullets
When the character is in this 'ADS bugged state' you can press LMB to fire rounds inside of the weapon, but there is no feedback, no sound, recoil or impacts etc.
In this video you can see I have 11 rounds in my MKII, when I enter the ADS bug I spam click LMB at least 11 times, seemingly nothing happens.
After putting the MKII back into my inventory and equipping it again, you can now see it says I have 0 (10) rounds.
After removing the magazine you can see that it wasn't only one round fired, but all of them, as the magazine count updates to 0.