We'd Just Finished A Supply Run, So I then wanted to check if we'd unlocked a mission. Upon taking out My MOC from the bunker, The second I drove it, It would turn invisible and the trailer part could not be entered.
I then told my friend to enter it from within my bunker instead. When he did so, He used the guns and noticed he was under the map, Just under Simeon's garage down by the docks.
I checked the map and this is where it said my MOC was, Despite me driving an invisible one.
When leaving the MOC, It could no longer be driven but wouldn't disappear. My friend left from the inside and spawned outside the invisible MOC.