I wanted to have mystical world on enigmatica 2 expert, but for some reason it keeps conflicting with JER.|
When I remove JER it works fine.
Crash Log:
https://pastebin.com/pZKFenUf

This is actually a conflict with Just Enough Resources and Stellarium/Stellars.

JER is creating a fake client world for its purposes and that other mod is attempting to create a capability for that level, but that is not compatible with JER's fake client world for some reason.