Blueberry flowers are less attractive to honeybees than most flowers, they really have to work to get nectar. Honeybees are also poor pollinators during cool wet weather. Hopefully you had some bumblebees around to get the job done. Other native pollinators like mason bees and sweat bees are helpful as well(small metallic looking bees).

Check pH it's possible it's drifted below 4.0.

Unless you are extremely limited with space I would try to get the plants in the ground instead of pots. Soil temperature around the roots should be much more stable for field planted bushes than container culture. Like the porridge in the story Goldilocks your soil in pots is always fluctuating from too hot to too cold sometimes in the same 24 hour cycle. In the ground they should be like baby bears just right.

I can relate. Two years ago I lost my best tomato crop ever, literally overnight, when the late blight blew in on a rainstorm.