I just lost rank, i was in a game at rank 5 then when the game finished i got "promoted" to rank 3. I've been playing since the closed technical alpha and this is the first time i've seen this happen
rank bug
"This is the progress wipe that was described in previous posts, to prepare the game for full release. You'll receive 1000 credits + 50% of what you had before, as well as an exclusive beta player tattoo."
this was after the wipe lol. like just now happened. but i realized when i joined another game i was rank 5 again so it wasnt permanent, just a glitch at the end of round screen.
you've probably joined a custom server where official ranks are not displayed. You also don't gain exp on those servers as far as I know.