Black Currant Getting Old?

The most serious problem with black currants is a mite that causes big buds to form and they also can give it an infection called reversion when the yield is greatly reduced. If you have good cuttings to replace it I would get rid of it after cropping. This has a bit about it.

https://www.gardenfocused.co.uk/fruitart...t-pest.php

If I see big buds on any black currant bush, I take a few cuttings off one of the others and then after a couple of years, get rid of my old bushes and replace with the new ones from the cuttings.