[1.21.1] Compatibility crash: Waystones onLoad in Sable stack; initiating action unconfirmed #1247

Clarification from the affected player

The affected player has clarified that the incident involved a portal from Iron's Spells 'n Spellbooks (installed version 1.21.1-3.16.3). The precise spell/item name and whether the crash followed creating, entering, or leaving the portal are not yet confirmed. This is a player report, not a controlled reproduction. The portal is the reported gameplay context; no direct portal-to-crash call chain has been established.

Waystones onLoad/sync is confirmed in the immediate exception stack. This does NOT establish that the player interacted with a waystone, or that Waystones initiated the incident. Iron's Spellbooks appears in the Level mixin list, but that alone does not establish causation either. A preceding action could potentially have caused chunk/block-entity loading; this is an unverified hypothesis. Root cause and which mod needs a fix remain undetermined.

Minecraft Version

1.21.1

Mod Loader

NeoForge 21.1.250 (dedicated server)

Describe the Issue

Our server crashed while a Waystones block entity was loading, with UnsupportedOperationException: Cannot change blocks in nonexistent plot holder thrown by Sable's block-change hook.

The observed call chain is:

WaystoneBlockEntityBase.onLoad:152 → BalmBlockEntity.sync:172 → ServerChunkCache.blockChanged → Sable blockChanged injection

The world saved during shutdown, but the JVM remained alive with a stuck thread warning and no game/RCON listeners. Restarting the unchanged server restored startup and ticking.

I have also reported the crash to Sable: ryanhcode/sable#1635

I understand the exception is thrown inside Sable, so this is a compatibility report rather than a claim that Waystones is at fault. Could you advise whether Waystones onLoad/sync needs any integration guard, or whether an existing addon/version is the intended solution for this case?

I found #1153 and #1229. Those concern teleport positioning/freezes and mention the Waystones: Sable addon. We have not tested that addon or established that it fixes this specific onLoad crash.

Environment

• Minecraft 1.21.1, NeoForge 21.1.250, dedicated server
• Sable 2.0.5
• Waystones 21.1.42, Balm 21.0.65
• Create 6.0.10, Create Aeronautics 1.3.2
• Sable / Stuff & Additions compatibility addon: sable_sa_compat 1.0.4
• Windows 11 amd64, Java 23.0.2
• This is a large modpack. Sinytra Connector 2.0.0-beta.17+1.21.1 is installed.

Reproduction status

Observed once on the running server on October 17, 2026 (server local time, UTC-7). We do not know the exact player action, whether the affected waystone was on a sublevel, or whether a sublevel had just been removed. No minimal mod set, test without Connector, or controlled reproduction has been completed. The stack trace identifies the call chain, but does not establish which mod should fix it.

Logs

Sanitized log excerpt, including the exception chain and shutdown outcome (not the full crash report): https://mclo.gs/I8xbQW0

The original crash report is retained privately; server paths and player details are not published.