Black dots in defocused circles

i’ve been experiencing a little quirk in my renders and I’m wondering what exactly is going on… every time I render out anything with circular blurs, I get these little black spots in some of the blurred circles. I’ve gotten these before, I don’t think it’s a lighting issue. I don’t know if it’s even an issue at all, I’m just wondering if there’s a way to minimize them. They kind of make the render look weird after you notice them. i attached a screenshot of part of an image experiencing the problem.

Bump. i thought I had fixed the problem but it persists… and ideas??