I'm seeing the problem here:
[00:13:15] [Server thread/INFO]: <Illoradannan> Guardians don't die without water
[00:13:23] [Server thread/INFO]: <SirWombat> nope
[00:13:27] [Server thread/INFO]: <SirWombat> they just hop around lol
[00:13:42] [User Authenticator #3/INFO]: UUID of player Illoradannan is 4bd91e4f-331d-4245-b824-bb2e2772c6d8
[00:13:42] [Server thread/INFO]: Illoradannan/138.210.198.121:60856 logged in with entity id 34244 at (101.6851987578056, 45.0, 203.68631042800547)
[00:13:42] [Server thread/INFO]: Illoradannan joined the game
User Illoradannan is not recognized by the server as logged out, yet she is logged out from the client. Illoradannan then logs back in and sees a duplicate of herself on the server. I've attached a screenshot of the issue. (Edit: Removed duplicate image. Didn't realize I'd already posted said screenshot.)
Added the latest server log that exhibited the problem.
Crash report added, as requested by Kumasasa .
I understand. Thank you for your help in diagnosing this.