Blueberries do have specialist pollinators! 😀
Other bees can pollinate them too, but they are not so good as the specialists.
This is quite comprehensive, albeit for North Carolina:
https://pollinators.ces.ncsu.edu/news/blueberry-pollination-the-role-of-specialist-bees/
As for stresses... they might also be reflecting stresses that happened on the prior year.