Fell into a gap, got stuck and had to die/respawn to get free.
Reproducing->probably just walk in there, i was playing ogryn which may be required as the other models are smaller and might fall through the bottom.
Havnt yet learned the name of this place, its the section with the shacks and stairs, we were moving down it when this happened if that makes a difference due to how the section are stitched depending on route in the mission.
On steam.