Worlds are not upgrading correctly from 1.20.1 -> 1.20.4

[TheDeafCreeper]

Describe the issue
When upgrading a world from 1.20.1 -> 1.20.4 the world ends up empty instead of containing the correct chunk data.

Logs do not indicate any issues

[05:21:50] [Server thread/INFO]: TheDeafCreeper issued server command: /swm load Hub
[05:21:50] [Craft Scheduler Thread - 11 - SlimeWorldManager/INFO]: [SWM] Loading world Hub.
[05:21:51] [Craft Scheduler Thread - 11 - SlimeWorldManager/INFO]: [SWM] Applying datafixers for Hub.
[05:21:53] [Craft Scheduler Thread - 11 - SlimeWorldManager/INFO]: [SWM] World Hub loaded in 2146ms.
[05:21:55] [Server thread/INFO]: TheDeafCreeper issued server command: /swm goto Hub

An earlier 1.20.4 build (I'm not sure which, every version I've tried so far failed, it was before the arrow fix though) did successfully convert worlds, and the updated worlds are correctly loaded on the current 1.20.4 server if already converted.

Spigot version
1.20.1 Server [SlimeWorldManager-15169 (MC: 1.20.1), Git 191c7b2 on paper_upstream]
1.20.4 Server [SlimeWorldManager-15616 (MC: 1.20.4), Git: b8f20c5 on paper_upstream]

Plugin version
1.20.1 Plugin [2.10.0]
1.20.4 Plugin [2.10.0]

How to reproduce
Create a world using SlimeWorldManager-15169, then try to update to 1.20.4, the world should lose all it's chunk data.

Crash reports (if available)

[TheDeafCreeper]

Actually I think this is related to https://discord.com/channels/741733106930810950/1185354365205229698
I tried another world and got this:

[kyngs]

We're aware, this is going to be fixed by the v12 PR (#91)

[kyngs]

@TheDeafCreeper The PR has been merged, can you please obtain the latest develop build and test whether this still occurs?

[kyngs]

Stale, probably fixed