Datafixer (DFU) runs during chunk/structure deserialization and hangs the server on Integrated Dungeons & Structures NBT (NeoForge 1.21.1, 4.4.2)

[bailboy101]

Environment

Minecraft 1.21.1, NeoForge 21.1.233
Brewin' And Chewin' 4.4.2+1.21.1 (NeoForge) — latest available build
Sinytra Connector 2.0.0-beta.14 present
Conflicting mod: Integrated Dungeons and Structures (idas 1.13.7) / integrated_api 1.7.3
Java 21.0.6

Summary

B&C's DataFixerUpper fixer (introduced in 3.2.0, per changelog used for renaming scarlet_pierogies) appears to be registered against a data type that also gets invoked during chunk deserialization of saved structure pieces. When a chunk containing an IDAS structure template is loaded, the read is routed through BnCDataFixer.updateWithFixers, which performs a full read-and-rewrite of the structure NBT and hangs (or runs pathologically slowly). The chunk never finishes loading; under a forced synchronous load (e.g. a player teleporting in) the server watchdog kills the server with a multi-second/"60368720 seconds" single-tick stall.
Steps to reproduce

World with IDAS structures generated.
Load (or teleport into) a chunk containing an IDAS structure piece.
Server hangs in the datafixer; watchdog fires, or the chunk silently fails to load.

Removing B&C resolves it. Re-adding B&C reintroduces the hang on still-unread IDAS structure chunks, confirming B&C is the trigger. The conflict requires both B&C's datafixer and IDAS structure NBT present.
Relevant stack trace (abridged)
java.lang.Error: ServerHangWatchdog detected that a single server tick took ... seconds
at net.minecraft.nbt.CompoundTag.shallowCopy
...
at com.mojang.datafixers.DataFixerUpper.update
at umpaz.brewinandchewin.common.utility.dfu.BnCDataFixer.updateWithFixers(BnCDataFixer.java:59)
at net.minecraft.util.datafix.DataFixTypes...update (via brewinandchewin DataFixTypesMixin)
at ...StructureTemplateManager.readStructure
at com.craisinlord.integrated_api.world.structures.pieces.IASinglePoolElement.getTemplate
at ...ChunkSerializer.read
at ...ServerPlayer.teleportTo (FTB Chunks map teleport)

crash-2026-06-14_00.22.36-server.txt

[OskaFlightboom]

The real issue that is described in the attached crash report is not related to Brewin and Chewin and has to do with structure templates that appear to try to send a request that bottlenecks the TPS to a halt. This would be true when trying to render a new structure in a fresh chunk. In short Brewin and Chewin is NOT THE PRIMARY CAUSE. However, I have looked further down into the report and saw an underlying incompatibility. Brewin and Chewin 4.4.2 is meant to be utilised for Farmer's Delight 1.2.X, the server currently loads v1.3.2 which is a major update that rewrites many tags. Currently there is no official version of Brewin and Chewin 4.4.3 that addresses the changes made in Farmers Delight 1.3.X, a community created version exists and is available here:
https://github.com/OskaFlightboom/BrewinAndChewinForNeoForgewithFarmersDelight1.3.2
This will fix your secondary problem related to Brewin and Chewin. For your primary issues I recommend reviewing all the compatibilities and dependencies of mods that make use of StructureTemplate. I recommend removing connectors (sinytra in this case) between Fabric and NeoForge as these two modloaders were never meant to live together in one environment given their base code and are likely to cause the whole system to be extremely unstable and prone to TPS bottlenecks.