During the Railjack missions, if you are onboard a Crew ship when it explodes you are ejected into space but are half-archwing. The Archwing is invisible, you can still use the archwing abilities, but you use your normal weapon instead of your archgun. When you board any other ship you are stuck in this halfwing form until you melee to correctly re-enter frame-mode.
This bug is easy to replicate. Simply stay on a crewship when it explodes then head back to the Railjack. Tried it twice and it's happened twice so far.
I've not tried using melee in space yet. Though I am curious if I will fall down the map or if I will use Archmelee.
Plus side, it's showing off how badly I need to forma up my Archguns :P