My rabbits stopped eating Purina Show formula when last summer arrived.
Most of them stopped eating Manna Pro this year when summer weather arrived.
I now am transitioning them to Nutrena's Nature Wise Premium. They're eating it, they seem to be doing quite well on it, and to top it all off--it's CHEAPER!!!
Another thing to consider, though. Are they blowing out their coats while going into a moult? If so, that may explain why they're not eating. Give them a stick of celery every other day for a week or so. It's important to keep their apetites up.