The area right underneath my chin, front and center, was one of the last places to fill in for me. The areas on the sides of my chin, right next to that bare patch, are some of my thickest+darkest areas of facial hair. But yeah, that one patch, along with my mustache, came in last. But it did fill in eventually! I just trimmed my beard on either side of that bare patch but left the hairs there to grow so it looked like it was all about even and the same thickness.