This probably happens with every Minimap, happens when walking around.

The crashlog:
https://gist.githubusercontent.com/Kabaril/da13b1ee277e0e98ae9b18572f25a753/raw/f13747b0fecae1e8b10d872e48c63065323ce600/crash-2018-05-22_02.33.53-server.txt

Happens only with JourneyMap, Haven't occured on Antique Atlas for me.

The problem is really caused by JM being multithreaded and assuming that blocks directly from Chunk can be safely accessed from other threads. This is not true in cubic chunks.

Interesting, i didnt think that it would work at all.
The problem is i think caused by loading the chunk your in, but when it loads a chunk above the light changes and it cant process it.

Fixed by JourneyMap in version 5.5.4