Black Artifacts Under the Iris in MetaHuman Eyes

Hello everyone,
I urgently need help with the following issue:

For some reason, I’m getting black lines below the iris and along the edges of the eyes in my MetaHuman. It’s definitely not caused by lighting, as I have already tested and changed the light setup multiple times.

I also tried changing the Material Blend Mode in BP_MetaHuman → Face (Material No. 5) to Additive, but the problem still remains.

Does anyone know what might be causing these black lines or how to fix them?

Thank you in advance!