They can use some extra protein while they're recovering from a molt. I changed them all to a grower with oyster shell available because many of them are moulting and only 4 are laying, the BA and BO. This increases the protein and doesn't burden them with calcium they don't need. The shells on the eggs I do get remained nice and hard. If you are not keeping food available during all the hours they have light, including when the light is on, that could be the problem. If you added light but it's not on a timer, the continuous light will stress them, which can definitely affect laying.
I have one who finished regrowing her feathers over a month ago and she has sill not returned to laying. She used to lay a good solid 6 per week; she is my leghorn. I don't add light and they are free range. I penned them for a couple of days to be sure I wasn't missing a nest somewhere, to no avail. She is about 1.5 years.
Even the ones who layed fairly well their first winter will typically slow down or stop their second winter, and this is my leghorn's second winter. I figure she'll hold out a while longer, maybe til spring, then I'm curious to see how she does.