My bucks never bred in a colony, had to remove the doe to be bred to a different, caged buck. Have two colonies right now, test pair and the dinner rabbits. After the first day or two of being introduced, the bucks have fully stopped attempting to breed. They know the does wont let them, they don't bother.
There seems to be a ton we don't know about rabbits. It might be possible for them to delay a pregnancy, to store sperm like some animals do, easy for them to reabsorb or terminate a litter at any point.
Poor nutrition or hidden illnesses do cause them to not get pregnant, absorb or abort or even produce smaller and runty litters.
I don't see how a new breeding would cause a doe to absorb any current that's growing, though. Secondary pregnancy seems to be possible.