Hello there @lil_wool69!
From your description, there’s a particular asset in your project (or even more than one) that’s triggering a mesh error, which can have mutliple causes, like invalid collisions, non-manifold geo, or corrupted data. That last one is the most likely, as you are working with APEX destructible meshes.
So, the packaging error is most likely caused by invalid geo from an APEX asset, meaning the first step would be to identify which mesh is causing it. You can check the extended log, and look for references to the cultrip (or even share said log here, we can help you figure it out). If nothing’s found there, then the best approach is to temporary remove all APEX assets from the project, and re-add them in batches, while testing packaging.
If there are too many assets to remove from your project, you can work the other way around, by opening an empty, test scene, and start adding the APEX assets one by one, until the faulty one is found.
When you find the affected mesh, you can try removing any custom collision set on it, and replace it with a Simple Collision. Also, if this asset is among the ones worked/merged in Blender, I would export it out of UE, and back to Blender for a revision:
- Look for non-manifold geometry (via Mesh > Clean Up > Merge by Distance)
- Check for any inverted normals (recalculate normals outside)
- Ensure the asset has proper scaling (apply all transforms)
- Review the mesh for no overlapping or duplicated vertices
- Avoid ultra-thin geometry, you can use a solidify modifier to give it a bit of thickness
After that, export it back, check collisions once again, and test for a new package.
Finally, after that many changes, you can always apply a bit of maintenance in the project. From your content browser, select your Content folder, right click on it, and apply “Fix up Redirectors”. After that, close UE, go to your project’s main directory, and delete folders Intermediate, Saved, and DerivedDataCache, for a full cache clear. Then, re-open the project, and allow it to rebuild.