Sorry for the late answer, but for anyone that might have this issue as well, here are some solutions I have used:
Fix geometry (NaNs, degenerate faces, zero-length normals).
Ensure correct export settings (Normals & Tangents) - export from 3D software.
Disable Unreal auto-calculations if needed.
Clear cache & restart Unreal before re-importing.
In my case it was due to the wrong mesh configuration inside the 3D software when one of the modelers made the mesh. Also importing logic had build mesh settings logic run by a py script that had this code:
settings = unreal.MeshBuildSettings()
settings.recompute_normals = False
settings.use_high_precision_tangent_basis = True
In conclusion, the imported mesh may contain extra parts that were incorrectly exported due to incorrect normals or unexpected geometry issues. These problematic elements can cause Unreal’s import calculations to fail. Fortunately, Unreal provides specific warnings or error messages for the meshes that fail to build. By checking the log output, I was able to identify the exact problematic meshes across multiple models.