https://paste.fedoraproject.org/paste/jNwboscOHWE5lSNkJJdFnA

I don't know what the users were doing at the time, we just added the mod to the pack.

2018-02-04-1.log.gz

One of your other mods has a thread which is messing with the world entity list. This is the line:

world.getEntities(EntityCoupleableRollingStock.class, EntitySelectors.IS_ALIVE);

I am doing that inside of the world tick handler on the main thread. Not sure what other mod has a thread spawned which is messing with that list.