1: Run or jog
2: Crouch
3: Immediately tap right click to try to raise your weapon

This leads to your character not raising their weapon but able to move but stuck in dysynced movement, however if you change stance you immediately raise your weapon. It can also be broken out of if you hold your weapon and press shift (or Middle Mouse Button) sending you into Off-Hand aiming allowing you go back to ADS. However doing the steps above again can still result in this issue.

Tapping right click to ADS after you crouch is not always necessary, as long as you aim your weapon after you crouch.

This can replicated backwards by crouch running and trying to raise your weapon after you stand.

This does not happen every time but it seems to happen every 5th or so time I do it, but can still be replicated a number of times.