I'm surprised that searching "gun glitch" didn't turn up the result I was expecting, seeing as most players refer to this extremely common glitch as the "gun glitch" or "weapon glitch"

Every once in a while, you will encounter a player who is stuck in the animation of a player stood up and switching weapons. This is extremely annoying since

• you can not see whether the player is holding a weapon or pointing it at you
• you can not see whether the player is firing the weapon
• you can not see whether the player is standing, crouched or prone (if player is prone you will miss when shooting point blank at his head)
• you do not know what weapon the player is holding
• you can't get a clear indication of how the player is moving, since it looks like he is ice-skating along the road

It turns out not everyone will see the same player doing this glitch.
Example:
Player A will see player B do it, but Player C and D do not
Player C sees player A do it, but players B and D do not
And so on.

The only way to "fix it" is if the affected player changes weapons. This can, in turn, create the same glitch for a different player.
Example:
Player A sees player B do it, Players C and D do not.
Player B switches weapons
Player C sees player B do it, players A and D do not.

The overall result of this is that you can not be friendly to an affected player because you can not judge his actions at all. It can also mean a serious disadvantage in a fire-fight, since a prone player looks like he's standing. Also, being prone or crouched behind a concealment is pointless, since some players can see your head (since they see you as standing, not crouched)