Missing head scales

Do we know what causes the occasional missing head scale on some corns? Or rather, it's not really a 'missing' scale, but it's more like the scales covering the head are rounded at the edges and don't meet in the middle. I think I've noticed it mostly in amel types, but occasionally in other morphs as well. In my collection, I have two corns with it to various degrees. Both have had it since I got them as hatchlings.

Lava and Peppermint with scale gaps on their heads.