Unsure how to fix this issue, I think it's an error with the model rather than the rendering etc. Pictures and blend file below.
Blend file link: https://drive.google.com/file/d/1H5YWCA17R-F8dchNgzOp-0T7lf74skoQ/view?usp=drive_link
Image link: https://drive.google.com/file/d/152vVv0OYMs09xdDa-d-pQMV7EJ_P9SaH/view?usp=sharing
Hi SStoic ,
When you Delete that black triangle, you can see, that there is a larger Quad underneath:
So the 2 Faces were partially overlapping (where it Rendered black).
Connect the 2 opposite Vertices of the Quad (over the short diagonal) with J. That fixes it.