Mentions Extrahardmode

https://pastebin.com/05xkFjBU

My offhand guess is that this error seems to look like a side effect of the player not being able to be placed in the world, so the player wasn't ever intialized fully, and as such you get that error while the player is already being disconnected.

if you can provide more of the log directly in this ticket, that would be helpful, or use https://mclo.gs