Before reporting:

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Also, please give this issue a descriptive name that contains the game version in the title, eg.: "[1.16] Distillation Tower Interaction Crash"

Description of the issue

An error occurred when the server started, and it could not be started.
I guess this may caused by List is out of sync caused by asynchrony ? idk...

Versions and Modlist

Minecraft: 1.16.5
ImmersiveEngineering: 5.0.0-135
ImmersivePetroleum: 3.3.0-4
ModList: Following the crash report

Crash Log

https://paste.ubuntu.com/p/tnnhpn6577/

Screenshot(s)

Images say more than a thousand words, so if you are bad at explaining things like me, throw in some images to accompany the What happend? section above.
(Perhaps you could even reference them in that section too)

Thanks for your reply!!!

I deleted some mods:
ClientTweaks
drippyloadingscreen
fancymenu
konkrete
performant
ponderjs
shutupexperimentalsettings
Tips

And it works well now...
Maybe they have a conflict?
These are some mods that should only be loaded in Client, I put them to Server wrongly

It crashed again, and I try to use ImmersivePetroleum-3.3.0-6, it crashed too:
https://paste.ubuntu.com/p/VbrygcqyzD/

the source(meaning the offending object in world) of both crashes seems unrelated, the later one happened while spawning something from IP in the nether while generating a new chunk

They all happen when the server is starting

did you change/update/replace/add a mod recently?

Just delete the mods that should only be loaded in Client,and update ImmersivePetroleum to 3.3.0-6

the second crash report went off by some data fixer and that is why it might be unrelated to the first crash

at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:1104) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:APP:kubejs-common.mixins.json:MinecraftServerMixin,pl:mixin:A,pl:runtimedistcleaner:A}

this seemed to stem from kubejs, i suppose their data data fixer interaction is broken too ...

So...What can I do...?

I got a new one:
https://paste.ubuntu.com/p/PSbJMxp384/