First off, you really shouldn't be adding so much heat to your coop. Chickens can acclimate to cold temps if given the time throughout the fall. So now that they can not tolerate temps below 40 degrees, they are stuck inside the coop, which is really not good for them. They need fresh air and exercise to keep them healthy. Too much hanging around in the coop will lower their resistance to lower and cause them to be open to bacterial infections and such.
So you might first want to start lowing this heat over the next month or so, so they can tolerate your average day time and night time temps. Should you lose power in the night right now, it could kill your birds.
BUT...all this being said, a molting chicken can lose their appetite. They don't lay during molting generally. Most of my birds lose the desire to eat much and will skip eating even their favorite treats or goodies. But during a molt, a chicken needs high protein. And if they are not eating much, they aren't getting enough of it. So I like to feed some cooked ground beef or ground turkey a few times a week. Feathers are 85% protein and the birds need a ton of it during molting. So the meat helps out greatly, especially when they are not eating a lot.
Also, you might try dampening the layer feed. Chickens much prefer damp feed to dry feed. This will help them eat a bit more.
Good luck in this cold snap. I will add heat to my coop, however my birds are acclimated down to an average of 5 or zero without heat. Should it drop to minus 40, I might add heat at this point.
Be careful of coop fires and stay warm!