Probably not eating it because of all the yummy treats you give. ;) If you stop the treats. They will eat normal food. Then, you can give treats once in awhile. :)
Maybe get them some all flock food and keep the treats to a minimum? They would still need grit living indoors and especially since they are not eating regular feed. Grit helps them to digest their food, so it is good they are getting it.
Is their crop empty in the morning? If so, probably just adjusting their crop.
If their crop is hard and full in the morning, then there might be a problem.
How often are they doing this? Do they have any other symptoms?
I noticed in the evening my girls will adjust their crop while roosting. The first time I saw it, I was researching every possible illness.