Black artefacts appear on imported mesh

Hi there

I have ran into a few issues with a particular prop and I was hoping somebody can help me to resolve these issues.

  1. I have imported various meshes which creates a single building. I have applied a MI to each applicable mesh, however I have black artefacts appearing all over the mesh. I have turned off “cast Shadows” in the skylight and this seems to resolve the issue, however we need to run the level with “cast shadows” on so disabling it isn’t really an option. I have included images below.
  2. The mesh seems to flicker intermittently in and out in-engine. The mesh seems fine in play mode, but it keeps disappearing and reappearing when working on the scene.

I’d appreciate any help or advise you may be able to offer.

Thanks

Anybody out there who can help with the above issue?