ConcurrentModificationException

Describe the bug

Server crash.

To Reproduce

Unknown

Expected behavior

Less crashes :)

Additional context

https://gist.github.com/clienthax/afe81b62b7fd28a0ed8da1a830035462

Environment

Mod details included on crash report

• Minecraft Version: 1.12.2
• AE2 Version: rv6-stable-7
• Forge Version: 14.23.5.2838

Duplicate of #3800

Probavly sponge is the culprit here. But I also can't rule out compact machines 3. Unfortunatly we have big issues in reproducing the issue without sponge maiking it difficult to fix something, as it looks like sponge is doing some magic to ae2, that breaks it

@yueh How would you suggest I go about finding the mod doing off thread world loading?