A minecraft:timeline registry error after joining PicoLimbo (Velocity)

[UPSOKen]

EDIT: The command registry was a misconfiguration of another plugin, but this console error is still happening. Doesn't seem to cause any major issues though. Just leaving this up incase it's something anyone cares to look into.

Describe the bug
PacketEvents throws an exception while handling registry synchronization when a player connects to a PicoLimbo server through Velocity. The error occurs during the configuration phase and results in the player STILL connecting to the PicoLimbo server, but command registration doesn't seem to work at all.

The exception indicates a failure to read the minecraft:timeline registry, caused by an UnsupportedOperationException inside PacketEvents.

---

Software brand

• Proxy: Velocity 3.5.0 (Build fix: Block State 1.19.4 #585)
• PacketEvents: 2.12.0 (installed on Velocity)
• Main Backend: Paper (latest version supporting Minecraft 1.21.11 / 26.1)
• Limbo server (Error appears when moving player to here): PicoLimbo (Docker image)

---

Plugins
Proxy (Velocity):

• PacketEvents
• TAB
• Velocity Scoreboard API (channel injection present in stacktrace)

If needed, I can provide a full plugin list.

---

How To Reproduce

1. Start a Velocity proxy with PacketEvents 2.12.0 installed
2. Connect a Paper backend server
3. Configure PicoLimbo as a fallback/limbo server
4. Join the proxy with a modern Minecraft client (1.21.11 / 26.1)
5. Trigger connection to PicoLimbo (e.g., during server switch or fallback)
6. Observe console error.

---

Expected behavior
PacketEvents should properly handle or safely ignore the minecraft:timeline registry during synchronization without throwing an exception or preventing command registration.

---

Screenshots/Files
Relevant stack trace:

[WARN]: PacketEvents caught an unhandled exception while calling your listener.
java.lang.IllegalStateException: Error while reading registry minecraft:timeline
...
Caused by: java.lang.UnsupportedOperationException
    at StaticAttributeType.getValueCodec

Full stack trace available here: error.txt

---

Additional context

• The issue appears specifically when handling newer Minecraft registry data (minecraft:timeline) introduced in recent versions.
• The failure happens inside PacketEvents registry decoding (TimelineTrack / AttributeModifier chain).
• Multiple plugins inject into the Netty pipeline (TAB, scoreboard API), but even after updating them to latest releases - error still occurs. It seems PacketEvents is the source of the exception (Or possibly an issue with PicoLimbo, but this was not happening before moving to 26.1 versions of PacketEvents and PicoLimbo).

[UPSOKen]

The command registration may be unrelated to this error. I have been trying to determine the issue for the past couple of days. Will close this if I determine it was something else, but so far - the only error I see is from PacketEvents.

[UPSOKen]

Command registration issue was a different plugin 🤦

The error message still persists though, but doesn't seem to effect anything.

If not worth looking into - feel free to close this bug.

[EinJOJO]

having the same issue with all plugins up to date.

[bobhenl]

Hello, I'm confirming this issue too, when using PicoLimbo