Unknown Crash, Exception Ticking World

[Pixel243]

I was hoping I could get some help with this weird crash. I've hosted many servers before and never had this issue.

Now and then the server crashed with "Exception ticking world". Everywhere I looked I rarely found any info on it (usually found ticking entity instead).
Any advice I did get (mostly from the modpack owner's discord) was "We don't know and it's near impossible to find out what it is".

Here is the crash report:

 

Description: Exception ticking world

java.util.ConcurrentModificationException
    at java.util.HashMap$HashIterator.nextNode(Unknown Source)
    at java.util.HashMap$KeyIterator.next(Unknown Source)
    at net.minecraft.entity.EntityTracker.sendLeashedEntitiesInChunk(EntityTracker.java:386)
    at net.minecraft.server.management.PlayerChunkMapEntry.sendToPlayers(PlayerChunkMapEntry.java:162)
    at net.minecraft.server.management.PlayerChunkMap.tick(SourceFile:165)
    at net.minecraft.world.WorldServer.tick(WorldServer.java:227)
    at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:756)
    at net.minecraft.server.dedicated.DedicatedServer.updateTimeLightAndEntities(DedicatedServer.java:397)
    at net.minecraft.server.MinecraftServer.tick(MinecraftServer.java:668)
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:526)
    at java.lang.Thread.run(Unknown Source)

 

If you want the full version, I can link a pastebin if needed.

Modpack link: https://www.curseforge.com/minecraft/modpacks/multiblock-madness

Some helpful information is that:

It seems to only happen when I leave my void world to enter the overworld.
Only happens 5-10% of the time.
Only happens when leaving the void world, and only the void world.

I know it's a slim chance someone could help, but it'd be greatly appreciated.

[TileEntity]

Also add the latest.log from /logs/

[Pixel243]

22 hours ago, TileEntity said:

Also add the latest.log from /logs/

Here is the end of the log. it was way too big to put in pastebin, but I started from when I was online and everything was fine. Error should be in here:

https://pastebin.com/Sdhdq593

[TileEntity]

Maybe an issue with ebwizardry

[Pixel243]

14 hours ago, TileEntity said:

Maybe an issue with ebwizardry

What in particular? I barely used that mod this time around, and it's never been a problem in the past.

[TileEntity]

This is the last line before the crash:

[ebwizardry]: Synchronising spell emitters for PixelTraveler

But I have no idea what this means

[Pixel243]

38 minutes ago, TileEntity said:

This is the last line before the crash:

[ebwizardry]: Synchronising spell emitters for PixelTraveler

But I have no idea what this means

that happens every time I enter a new dimension.

[TileEntity]

I have no idea

[Pixel243]

UPDATE:

This seems to be happening every time I leave the Beneath dimension (2 for 2).

Not sure why those 2 dimensions specifically. I have no problems with the nether or Twilight Forest.