Initial Questions

• I have searched this issue tracker and there is nothing similar already, and this is not on the list of known issues. Posting on a closed issue saying the bug still exists will prompt us to investigate and reopen it once we confirm your report.
• I have verified that this issue occurs in a SUPPORTED environment, meaning I can reproduce this WITHOUT OptiFine, and without Bukkit+Forge server software like KCauldron, Thermos, Crucible, Mohist etc

Mod Version

2.6.2

Describe the Issue

Server has crashed, but i have no idea why :(

Crash Report

https://gist.github.com/avescarelo/cc9d3cbb04d73c1ccefc30ad82a54b1c

Crucible is not supported

As this code normally cannot produce ConcurrentModificationException I believe the issue is on their end. Please report this conflict to them

For the record, don't check that the issue occurs in a supported environment when you are not in a supported environment.