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Error when displaying potion with custom potion effect (Protocol1_21_11To1_21_9, CONTAINER_SET_CONTENT (0x12)) #1193

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Error when displaying potion with custom potion effect (Protocol1_21_11To1_21_9, CONTAINER_SET_CONTENT (0x12))#1193
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@nosatlev

Description

@nosatlev
nosatlev
opened on Jan 24, 2026

/viaversion dump Output

https://dump.viaversion.com/376edd4e1c584e9b3e3ecd7014ab2cd3c22e4f78ee0c4c85c1a9193dd83e3a58

Server/Client Error

Server Error: https://mclo.gs/5OpzLzA
Client Report: https://mclo.gs/pdk3BDe

Bug Description

When player joins the server with ViaBackwards with client version below <1.21.11 and server is 1.21.11, using potionMeta.addCustomEffect(new PotionEffect(type, duration, amplifier), overwrite) with some potion types and displaying that potion to player causes player client to disconnecting from server with kick reason: Internal Exception: io.netty.channel.unix.Errors$NativeIoException: recvAddress

PotionMeta meta = (PotionMeta) itemStack.getItemMeta();
meta.addCustomEffect(new PotionEffect(type, 3600, 0), true);

This issue appeared after updating server's version to 1.21.11.

Logs: https://mclo.gs/5OpzLzA

Steps to Reproduce

  1. Join with 1.21.4 client on 1.21.11 server
  2. Open a custom menu with list of potions

Additional Server Info

PaperMC 1.21.11

Checklist

  • Via plugins are only running on EITHER the backend servers (e.g. Paper) OR the proxy (e.g. Velocity), not on both.
  • I have included a ViaVersion dump.
  • If applicable, I have included a paste (not a screenshot) of the error.
  • I have tried the latest build(s) from https://ci.viaversion.com/ and the issue still persists.

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