What I suspect is that as the BR develops, the berries drop from being diseased(it could also be anthracnose- they look similar). They aren't really missing, it's just natures way of dropping the bad seeds. Hope you get a good crop.
NW I just got in a 1600 foot roll of VineSide Netting. The kind that you put on each side and attach the top and bottom. Hope it works well. I also have 1500 feet of 14' bird netting coming.