Steps to reproduce :
Have a custom lobby with more than 4 players
Launch a game with 4 players
On the result screen, have the spectators spam the X (the emote in result screen button) (and MAYBE the Start button at the same time), on the CSS they will be in playtest and be able to play in the game.
You can now launch with more 4 players :D
A clip from a glitched lobby : https://medal.tv/fr/games/rivals-2/clips/kQ0OdSFDRWRXYNwBN?invite=cr-MSwxQXQsNjA3Nzk0OTY&v=10