ArrayIndexOutOfBoundsException crash on 1.20.1

[abby-cadabra]

Bug Description

Hi there!

I'm on Forge 1.20.1 with ModernFix 5.20.2. I'm running a custom collection of around 350 mods.

I've been dealing with a persistent crash in recent days. Basically whenever I teleport to another area away from my base (using either Waystones or Xaero's map), I get a crash due to "exception ticking world," due to java.lang.ArrayIndexOutOfBoundsException. The crash log also references PersistentEntitySectionManager. Sometimes the game will just crash straight to desktop, while other times it will hang and need to be aborted manually.

I've tried disabling various mods that I thought might be the culprit (Distant Horizons and others) with no success - until I tried disabling Modernfix. Now I can load into distant chunks without crashing.

Very possible that the crash is actually caused by something else and Modernfix is just the catalyst, but figured it might be useful information anyway. I've attached my crash log below.

Reproduction Steps

Have ModernFix enabled

Teleport to a distant chunk using any means

Crash immediately

Log File

2025-02-05-2.log

[embeddedt]

I'm not sure what keeps causing these crashes for people; I suspect another mod is accessing things on the wrong thread and conflicts with one of my mixins. Anyways, can you try this test build and send me the log from when it crashes?

test_build.zip

[vizthex123]

I've got a similar crash:

latest.log

Very frustrating, as I've wasted like an hour trying to figure out wtf is wrong.

[embeddedt]

Your crash looks unrelated; it seems to be an issue with Thermal loading magmatic dynamo fuels.

[vizthex123]

i finally figured out it's because of a KubeJS script i wrote ffs. Removed a mod and forgot i'd used items from it in TE's dynamos.

[abby-cadabra]

Hello, thanks for looking into this!

I tried your test build - crash log is attached :) Hope this is helpful!

2025-02-05-6.log

[embeddedt]

This log makes even less sense than the previous one. It looks as if you have another mod attempting to worldgen on a different thread. Maybe try removing Distant Horizons/similar mods, and see if the test build produces a better crash?

[abby-cadabra]

Cheers - here is the crash log with DH removed and with your test build enabled. I don't think it says anything different, so far as I can see.

crash-2025-02-07_09.13.12-server.txt

At a bit of a loss re: what else to try. I have quite a few biome/structure mods, but I imagine if I start removing them it will probably just crash anyway and I won't learn anything useful. Definitely a tricky one.

[ITSLOCKED]

i dont know if my log helps, but ive basically been getting the same exact error. the first time it was an NPE, and this time its an ArrayIndexOutOfBounds. it still falls under the same “Exception ticking world” error. the only pattern I can see after doing a bit of research to see if anyone else has this problem, is that companion is present inside their crash logs same as with mine and abby's crash log.

this is the crash that occured the first time along with the server logs

crash-2025-10-04_18.03.05-server.txt

2025-10-04-3.log

after attempting to restart the server another crash occurred involving watch dog, this pattern repeated every time the same Exception ticking world crash happened

crash-2025-10-04_18.04.05-server.txt

2025-10-04-5.log

after a 3rd restart the server launches just fine unless the same exception ticking world crash happens again.

it should be noted that i am on fabric 1.20.1 and not on forge but the same mods that i noticed in the other crash logs were still apparent (modernfix, companion)

and also here is the crash involving the NullPointerException

crash-2025-10-02_23.08.35-server.txt

this NPE crash stopped showing up after removing Mobtimizations but i am now faced with the crashes above