Players with drones are having a major known issue with 20.4 where they get an error repeatedly until eventually they cannot login to the server.
ERR NCSimple_Serializer (ch=0):
EXC Memory stream is not expandable
I have read that deleting drone data or player data can fix it temporarily but that essentially if a player has ever had a drone they get the error. Myself i put my drone in a chest and the error happened less frequently but then eventually it did happen and now it occurs on each login preventing character creation.