Crash log:

https://pastebin.com/Bs4GnQi3

step to produce:
1. load normal MC server

2.set /gamerule spawnRadius 5000 or higher

3. die to mobs 5-10 times until respawn button doesnt work. server should then time u out

3.5. if u stay off server and look in task manager you will notice excessive cpu usage refering to a memory leak, this will not stop until someone logs in.

4. login back in server and server should instantly crash with this log error.

i dont know if this can be re-created in single player.

i also do play the server on same machine as client - working on setting up server for friends