How to Fix a Crash Caused by Overlapping Mixin Features

Recognize the Symptom

Overlap crashes typically appear during early startup, before the main menu. The log usually names a mixin service, a duplicate provider, or a loader that failed to initialize because something was already registered. If you recently added a second mixin loader or the UniMixins combined jar next to an existing loader, that is almost certainly the cause.

Diagnose Which Side to Remove

Ask which loader you want to keep. If your existing loader already covers your needs, remove the UniMixins combined jar and add only the individual modules you are missing. If UniMixins covers everything, remove the other loader entirely and keep the combined jar.

The Modular Fix

Because UniMixins exposes each feature separately, the cleanest repair is to stop using the combined jar when another loader is present. Replace it with only the specific module jars that provide features your other loader does not. This eliminates the duplicate service without forcing you to abandon either loader.

Confirm the Fix

Relaunch and check that the startup log no longer reports duplicate services. Then load into a world and confirm your mixin-based mods still function. If a specific mod stops working, you removed a module it depended on; add that module back and remove the equivalent feature from the other loader instead.