Hi there. I grow blueberries and have had the same issue. I can see if some of the flowers are producing fruit or if the entire plant is having the same issue? Also with more details i.e. watering, weather, blueberry type, amount of sun, I bet we can figure it out. In my scenario, I had multiple blueberry plants producing like crazy, except for one. I called my local ag office and discovered it was underground aphids. Blueberry roots are very sensitive to water PH, fertilizer, soil, you name it. I dug up some of the soil and sure enough. it was crawling with aphids. I have no clue if thats what’s going on with you but the advice below helped tremendously. I hope this helps. God Bless.

https://blogs.cornell.edu/berrytool/blueberries/blueberries-flowers-turn-brown/

no aphids in mine (but just to make sure, I'll dig a couple of them up and add some canadian peat etc ..) but aphids really not a problem in my garden (I spray neem oil and Diamacious earth) since there's plenty of ladybugs in the garden, since I grow most of my BB in pots, I think it lacks the micro nutrients like potassium etc .. also I started using Seabird Guano and bought some azomite and I'll find out next season if this helps retain my BB fruits

did you happen to have taken some photos of the root with aphids, just for FYI?

Thanks

Could it be due to a pollination problem? Some berries look good while others whither and die. Did you see many bees this year? My #1 pollinator here for BBs are Bumblebees and their cousins (mostly Carpenter Bees) that are in the BB bushes non-stop all day during blooming time.

That was another of my thesis, since weather here in CA has changed the last 2 season (hot cold hot cold in Jan, Feb March, I have seen a lot less bees than normal even this warmer days but what little bees showed up should have been enough for pollination so hopefully it's just lack of nutrients than bee's but won't know for sure until next season but for now, I will try to feed my plants azomite, compost, Seabird Guano and some alfalfa pellets, some elemental sulfur etc.. I love those Carpenter Bees, I see them year round in my garden alone with those pesky bluebirds that love my unnetted bb

It happens when the flower is not well pollinated or have some self incompability. Try adding another vaeiety that suits your variety and bees houses.