Got this report from a player, playing a modified version of ATM10 v4.2:

Game suddenly crashed after entering yung's mineshaft, I think probably related to the essence of knowing item

All the Mods 10 - 4.2 crashed. The logs have been uploaded to gnomebot.dev:

latest.log | debug.log head / tail (~15MB & ~88k lines) | crash-2025-07-09_04.54.44-server.txt | KubeJS: client.log / server.log / startup.log | crash_assistant_app.log | modlist.txt | CurseForge: skip launcher

Mod list changes beyond the modpack:

Added mods:
ash_api-neoforge-21.1.0.jar
badpackets-neo-0.8.1.jar
c2me-neoforge-mc1.21.1-0.3.0+alpha.0.71.jar
collective-1.21.1-7.84.jar
configured-neoforge-1.21.1-2.6.0.jar
dynamiccrosshair-9.3+1.21.1-neoforge.jar
findme-3.3.3-neoforge.jar
forgeautofish-7.1.0-neoforge1.21.jar
forgified-fabric-api-0.115.6+2.1.0+1.21.1.jar
fullbrightnesstoggle-1.21.1-4.2.jar
MaFgLib-0.2.2-mc1.21.1.jar
shuffle-neoforge-21.1.0.jar
tectonic-neoforge-1.21.1-2.4.3.jar
zergatul.freecam-2.3.1-neoforge-1.21.jar

Removing structure mods would not cause the problem because the structure data is wiped from the chunks when loaded and so, the code to get structures from chunk would not get the structure at all. It specifically has to be an unregistered structure or registry being broken

The modpack is broken. Specifically, it managed to break this.

The summary is, I get structure from the world itself. Check if that structure is in the structure registry in that same world. And would’ve been able to see if it is present in a tag.

One or mod(s) managed to have it where there is a structure in world, THAT IS NOT IN THE STRUCTURE REGISTRY. How that was achieved, I have no flipping idea. If you had a structure mod or datapack and then remove it later, the structure bounds in the chunk would be wiped upon loading so that could not cause the issue. Someone had to literally have unregistered structure spawning which is an incredible feat considering how worldgen structures have been datadriven json for so long.

You would need to go to where that person is crashing and find what structures are in that chunk and what mods they are from and report to the person to stop spawning unregistered structures. If their structures are registered, then it is worse, you got a mod that is breaking the worldgen registries themselves and the instances of structures in world does not match the instances in the registry anymore

Player added this info:

idk, before i got the essence of knowing i've been in the mineshaft a couple times with the same added mods, mod version & had no issues

also forgot to mention the crash happened right after i used the "eclipsegate wand" from justdire things in the mineshaft

this is what wand does:
https://www.youtube.com/shorts/JVEAjxguj7Y

Interesting.
If we had a mod that added certain structures and later we remove it, would it cause this crash? Because sometimes we have to do that, specially when something is broken and modder does not support it anymore.

Ok, thanks, will tell the player to get back to our original mods if they don't want this issue.

I would be curious as to what mod is being screwy as this could be an annoying issue for many and very difficult to track down. You can ask the player to join here if they really want to keep their set of mods but they gotta be willing to put in the time to debug it further

Tectonic is just a overworld overhaul mod by replacing vanilla worldgen files with more json files. It doesn’t change the actual fundamental workings of the chunk generator or its structures. So I remain doubtful it is tectonic. What structures are in the crashing chunks (at all y levels) and what mods are the structures from