Ran into this error with multiple mobs on newest snapshot, took me a while but I found a work around, have everyone log into the server one by one and see who joins last that causes it to throw errors, have that person put their stuff in a chest and then delete their player data and restart the server, you can find their player data through their personal UUID on the server. It shows it when they log in on the console, after deleting the player data restart the server and have them rejoin and port them back to their house, where they retrieve their stuff
Theodore Vaughn
Ran into this error with multiple mobs on newest snapshot, took me a while but I found a work around, have everyone log into the server one by one and see who joins last that causes it to throw errors, have that person put their stuff in a chest and then delete their player data and restart the server, you can find their player data through their personal UUID on the server. It shows it when they log in on the console, after deleting the player data restart the server and have them rejoin and port them back to their house, where they retrieve their stuff