Me and some friends are playing with IR and rftools Dimensions.
One of us was in a dimension that didnt get any power anymore and after the power ran out of that dimension, the server crashed.

My thought is: The algo which computes the next node ( java.util.HashMap$HashIterator.nextNode(HashMap.java:1445) ) crashes the server if a dimension unloads on a not normal way ( probably shutting it down ) while a player is still in that dimension.
We don´t have any rails yet, so i suspect that the algo is checking around the player even if nothing is there and a short time after the player left/died. This way it could have happened that it checked a non existing dim and crashed.
crash.log

If you don´t know how rftools Dimensions works: you can create your own dimensions with that mod which have to be powered. If the power runs out on that dimension, you´ll get killed and the dimension is getting shut down to save server resources.

My mistake; reopening ticket as I did not read correctly.

Upgrade to the latest UniversalModCore, I fixed the bug in there: https://www.curseforge.com/minecraft/mc-mods/universal-mod-core/files/3141762

Fixed the Issue, thank you all