Diagnosing prefab patch problems

Start with the authoring Inspector, then the effective preview, then pm_summary.log. Each stage answers a different question.

The JSON does not compile

Select the root PrefabPatchAuthoringMetadata component and click Compile JSON Now. The Inspector and Console list the invalid override.

Common causes:

  • an added GameObject has no PrefabPatchAuthoringObjectId

  • two added objects use the same ID

  • a referenced asset is neither linked nor a mod-owned Addressables entry

  • the variant is not based directly on a Redux SDK linked prefab

  • the selected Mod asset has no all-assets Addressables group

  • a component type cannot be resolved

  • an override cannot be represented by the current schema

Fix the variant; do not edit the generated JSON.

The preview fails

Open Effective Prefab Preview resolves all known patches for the target. Failures here usually mean a missing target, stale stock structure, unresolved reference, dependency cycle, or cross-patch target without NeedsPatch.

If the linked stock prefab changed after an SDK/game update, refresh or recreate the linked asset and recompile the patch.

It works in preview but not in game

Check the Prefab Patches section of pm_summary.log. Use the part for the feature set of the campaign that you tested. The summary has one part for each feature set that the session patched.

Confirm:

  1. your mod and all features in the Required Features of the patch are on in that campaign, and all features in Excluded Features are off. If the feature set does not allow the patch, the plan does not include the patch;

  2. the manifest was discovered under your mod's prefab-patch label;

  3. the patch was not removed by a missing need or active conflict;

  4. the resolved plan is valid;

  5. the game requested the Addressables key you patched;

  6. composition did not fail.

An APPLIED-style result means the plan ran, not necessarily that the game used the field in the way you expected. Test the actual feature that instantiates the prefab.

Another mod overwrites the change

Two different writes to the same property are reported as a soft conflict. The later deterministic operation wins.

Do not jump straight to Late/Last. Put both patches in the same pass and bucket and use AfterPatch against the specific patch when possible.

A custom component is missing

Make sure the assembly containing the component is part of the installed mod and that the owning mod is declared as a dependency. The component type must be available before the prefab is composed.

Useful identifiers

Keep the full patch ID, operation ID, target address, and diagnostic code when reporting a problem. Prefab diagnostic codes start with PM-PREFAB- and make it much easier to locate the failing stage.