I've looked at other posts. None of them have an answer. Just others saying this is happening to our chickens also.
We have a few hens with white tips around the head. There's no sign of mites or disease. Favus seems to be a skin condition by photos I've seen. The comb not feathers. Their combs are fine. Are they getting old and grey? They are 2.5 years old.
Molting? I can't see clear enough in the pictures, but if new feathers are coming in then the feather shafts can look like that, white bits will flake off as the new feathers open and the shafts fall away. It often looks worse around the head and face since they can't get to those with their beaks to preen and pick them off with their beaks. An extreme example on a roo below: