ISA is a highly selected, patented hybrid. If you truly have ISAa, (a lot of folks pawn off generic RSLs for ISA) then they will require a slightly better feed to be as productive as they can be. 300-330 eggs per pullet year.
It just may well be the move. Or worms. Or lice. But most likely, it is somewhat a combination. Start with more light, early in the morning. Have it come on at 4:30 or 5:00 am. Then, be sure they "like" the feed you are using, as that too is a change for them. A quality layer feed should have 17% minimum protein, and many do not. Not even the "name brands". You can always supplement with a scoop of Flock Raiser of other 20% formula. (although Flock Raiser has low calcium)
Finally, going to ZERO eggs is a flock wide shock of some kind. Having poorer grade feed might reduce size, weight and number of eggs, but normally doesn't just shut them down. I also hesitate to suggest that age is also a factor. Since this is a popular commercial layer, I trust you know for certain these pullets are under 9 months old, for certain.