Direct answer

After a Minecraft update, update protocol/packet libraries and every plugin that depends on them to versions explicitly supporting that server build. If the error disappears when the packet/protocol layer is removed on a test copy, report the incompatibility instead of forcing unsupported versions.

What it means

Packet APIs and protocol translations often change with Minecraft releases. A library such as Java Edition ProtocolLib or PacketEvents can load but still fail when a dependent plugin tries to read a changed packet type. ViaVersion-style protocol translation is a separate component; first identify which project produced the error and which plugin called it.

If you are a player

  • Copy the exact kick/error text and record your client version, server version if known, and the time of failure.
  • Test with the Minecraft version the server advertises; an older or newer client connecting through ViaVersion may take a different packet path.
  • If the issue happens only while opening a menu, seeing a hologram, joining a specific world, or using an anti-cheat feature, tell the owner exactly which action triggers it.

If you run the server

  1. Save the startup log and the full first packet-related stack trace. Identify the first plugin named in the Caused by chain and note the exact server build.
  2. Inventory installed packet libraries and consumers: for example Java Edition ProtocolLib, PacketEvents, ViaVersion, ViaBackwards, anticheat, disguises, holograms, or menu plugins. Do not assume these libraries are interchangeable.
  3. Check each project’s official release notes for your exact Minecraft and Java versions. Update the library and dependent plugins as a compatible set; do not install a random development build on production.
  4. On a copy of the server, reproduce with a minimal plugin set. Add the packet library, then its consumers in small groups until the offending combination is found. Never remove an essential plugin from a live network without checking consequences.
  5. Restart fully, reproduce the same client action, and compare logs. If no compatible combination exists, revert the server update from a complete pre-update backup or leave that feature disabled until its maintainer releases support.

References

Use the documentation for the exact software and release you run. These sources support the settings or diagnostic behavior used in this fix.

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