Happened to me 2 times. In first one I downed all 4 fireteam members when I tried to kill them my f button didnt work and started to crouch even though I wasnt pushing crouch button. Second time, I downed 3 members killed the first then f button didn’t work again but this time it got stuck on hold f loops. After they died on the ground I downed the last member and was able to kill him.