It's not only in pvp, i have seen it happening all over planets and in ops. Like the fight with gharj, all the islands you fight on, including the paths to the next are all bugged and say you can't crouch on them. (i did find one that worked, but that's insignificant compared to the whole fight) But from what it seems like is that if you are slightly above ground level it considers you too high and stops you from being able to use crouch exclusive abilities.. (could be wrong, but that is how it seems to me.)