I am getting this error around 50% of the time when starting up a Server + Players type of playtest
This error appears on the client that failed to join the game, and the character cannot be controlled + additional APIs will break.
Unfortunately, core scripts are now completely closed source, so I can’t give an insight into why this is happening, but I suspect it might have something to do with the fact that players have negative user IDs in these forms of playtests.