I consider myself a very lucky creator that the most controversial topic among OP’s readership seems to be the length/existence of Marek’s beard. There are two very opinionated camps who are sad or delighted when it has appeared or disappeared. Myself, I am in neither camp.
The reason the characters’ hair lengths change is as arbitrary as physical changes on anyone you know. Sometimes Marek decides not to shave when he probably should. Then he gets sick of it one day and it’s gone. Much like the more fashionable leftovers in your fridge.