Blackcurrants shrivel and go yellow / orange before maturity

[TrialAndError]

Hi folks,

Two people on my allotment have blackcurrants which have shrivelled and gone yellow / orange before they mature into proper black fruits. Any idea what is happening here? Run-off?
I'm concerned because I have blackcurrants as well (unaffected so far) as do other plot holders. Will this problem spread?

[roitelet]

I have had something similar happen to my Jostaberries. It has only affected the ones directly exposed to the sun. I haven't it down to sun burn as we have had very high temperatures and scorching sun.

Be interested to hear if there is another reason.