I was web surfing and dropped in on Local mycology group's website for fun. I started reading their last month's newsletter and came across explanation for some of my blueberries turning into "raisins" on the bush this year.
The berries looked perfectly fine, plumped up green, and started to color, but when I went to see if they were ready to pick, they had shriveled up into dry berries.
It's a fungal disease called "Mummy Berry" spread by the fungus Monilinia vaccinii-corymbosi, and apparently causing a huge crop loss in Oregon and is also present in NJ blueberries as well. Now, I know I have a serious problem to contend with. . I'm afraid I might have imported it with the pine bark mulch I bought and used this spring.
Here is the link to the newsletter https://njmyco.org/newsletter/NJMA_News_42-3.pdf
The article is on P. 3 and another reference and a good photo of offending fungus mushroom which appears earlier in spring, which may clue you in to potential problem in your blueberries is on P. 8.