yesterday I had a very wierd match on terminal where I was in some kind of spectator mode with Arty after the first death. I was able to run and shoot around as a player but invisible to others and I also could not receive or do any damage from/to others. When I threw my ammo packs they were invisible (to me) but players could pick it up normally. The supply XP (to me) was even given for both the red and blue team picking it up! So I guess I was in some neutral spectator mode thingy with the ability to run around and spam your abilities.
But here is another odd thing:
There was a player of my team who was playing with a default model.
I can not confirm that he was invisible to others likewise but this may be a cohesive issue. Maybe my player model looked the same…
Howsoever, the server I played on had some serious lags and delays.
When rejoining the match the issue had gone, so I guess it was a unique feature