on this server i play on owned by a Live Streamer there's a common glitch where sometimes a pokemon won't send out and will just do nothing, if you relog you will see your pokemon has either been replaced with 1 pokemon from your PC or just will be gone, your pokemon that was swapped would either be in an empty slot somewhere in your PC, in the slot where the pokemon that appeared in your party once was, or will just be gone as if you released it, it happened to about 3 or 4 players all at once at the same time and the streamer had to respawn them all back in, this was all on stream too, it would be very nice if you could fix this.
this is footage of the glitch happening, it starts at around 2:36:48 and lasts for about an hour,