you say the plants just started flowering, (auto Runtz?) IF deffo Photo's - stress flowering from being pot bound is my guess. If you don't pot them on there is a chance they wont re-veg and they go into early Senescence. Pot them on, it does not need to be a much bigger pot, use only a very very light feed until the leaves do their flip and you will be good to go. PS as gmslave advised as well.