This situation is caused by a trim curve that is somewhat bad and creates a surface that the mesher has problems with.
You didn’t include the original objects that you used to create this object and so it’s difficult to say exactly where it went wrong.
If you extract those surfaces and untrim them with the
AllSimilar=Yes options, you will get a shaded untrimmed surface and the trim curve for each of these.
In Rhino 7, there’s the
IntersectSelf command that will show you where this curve is bad - there’s a tiny self-intersecting loop somewhere.
It looks like you can fix the surfaces by running
SimplifyCrv on the curves and then trim the surfaces.
In this picture: a non-fixed surface on the right and a fixed one on the left with a point indicating where the self-intersection occurs.