Have been playing a server for a week and it has been fine but when I first entered the end it kicked me out and crashed the server.

Try resetting your end world:

Delete the "DIM1" folder from your world folder.

Quote from 1Snipes1

Whenever I enter the End Dimension on my server with a custom pack it ends up crashing the server and disconnects me. I have been playing for a week and it never happened, just when I entered the end it started.

I tried to make a single player world to see if it was the server and I was able to enter the end perfectly fine.

This is the Crash report: https://mclo.gs/WadXKMI

This is the Log I know there is alot of red: https://mclo.gs/MYaIGxl

Can you try removing lithium and see if it works