Why do the Blackcap berries dry?
Healthy-looking canes and leaves, good blossoms, but for the second year in a row the berries have formed and then dried up within about two days of formation. This has been localized to one patch, but it seems to be spreading. I acknowledge that many people try to eradicate black raspberries, but we enjoy ours. Birds like them, too.
It sounds like these are not purchased plants, but rather volunteers. It is common for wild canes to have diseases. We can't say for sure what yours are dealing with. You can send us photos of the plants, but you also may want to just rip out any that have problems so it does not spread.
Black raspberries are wonderful fruits and worth trying to manage, but when planting new plants we always recommend buying stock that is certified virus-free and removing all the wild plants nearby.