Yesterday I was playing a 'High Ground' coop mission, and stumbled upon a bug/glitch where if you get injured -> try to switch your gun -> start using armour plates after the gun moves off-screen -> get downed in the midst of putting an armour plate and self-revive, then you'll be able to (seemingly) run faster with no gun in your hands.

Clip with timecode (0:25) where glitch starts: