Mixin failures

InvalidMixinException: Unexpecteded ClassMetadataNotFoundException

What the log looks like

org\.spongepowered\.asm\.mixin\.transformer\.throwables\.InvalidMixinException:? Unexpecteded ClassMetadataNotFoundException whilst transforming the mixin class
InvalidMixinException:? Unexpecteded ClassMetadataNotFoundException

How to fix it

  1. Find the line saying 'Mixin apply for mod <modname> failed' or 'from mod <modname>' right above the error in your log to identify the broken mod.
  2. Check the exact file version of that mod (and any dependencies your launcher automatically downloaded with it, such as Sodium alongside Iris) and replace it with a build made specifically for your exact Minecraft version.
  3. Verify your Java version in the log's mod/system list: use Java 17 for Minecraft 1.18 to 1.20.4, Java 21 for Minecraft 1.20.5+, and Java 8 for 1.16.5 and older.
  4. If you are running a server with newly released JDKs (like Java 22 or 23) on an older Minecraft version, switch the server start script to point to the recommended LTS Java version instead.
  5. Update Fabric Loader, Quilt Loader, or Forge/NeoForge to the latest stable version for your Minecraft release so Mixin has up-to-date class reader support.
LoadersFabric, Quilt, Forge, Neoforge, Server
SeverityStops the game
CategoryMixin failures

Check your own log

Related errors

Mixin failuresCritical injection failure — a mixin could not find its targetTwo mods are usually fighting over the same game methodMixin failuresInvalidMixinException: Mod Mixin Failed to ApplyOpen your latest.log or crash report and look for 'Mixin apply for mod' or the 'Config :' line inside the 'InvMixin failuresMixin Transformation of net.minecraft.client.main.Main FailedOpen latest.log or the launcher crash output and look at the Caused by lines below Mixin transformation of netMixin failuresMixin apply failed — one mod could not patch the gameThe line names the mixin config, and its prefix is the mod id that brokeMixin failuresMixinExtras is missing or too oldUpdate the mod that needs it — modern mods bundle MixinExtras themselvesMixin failuresMixinTargetAlreadyLoadedException: Required Class Loaded PrematurelyRename your SpongeForge JAR file in the mods folder so it begins with an underscore or 'aaa' (for example, '_s