Thickness baking issue

Sastrei

I'm baking a thickness map and getting weird squares across much of the resulting texture, though my main concern is the windscreen in the bottom left corner.

I've checked normals to make sure they're not facing inward on either the high or low poly, and in any case those squares are much smaller than the actual polygonal face being baked on either high or low. I've tried increasing and decreasing the cage ray distance, the issue remains.