Slosh's fix is something I've come to rely on when I have a similar issue. Sometimes there's just something corrupted in there, and it's easiest to just delete it out. A mesh cleanup operation may help as well. Principle is, if there is a dumb, easy solution, try that first before going into hardcore troubleshooter mode.
I'm having an issue with normal map bake, and I've exhausted all options I can think of. This pinch and seam on a simple flat surface will not go away. I have baked this in Marmoset, Painter, and xNormal with every setting possible, with and without a cage. Hard edges, soft edges. Object space and world space normal maps…