Blossom drop post-pollination

Alright guys, I could use the abundant expertise of this sub right now.

What could cause widespread blossom drop of pollinated tomato blossoms?

I have eight tomato plants on my balcony. Some in 5-7 gallon pots (yes I know, that’s small), and some in 20-25 gallon grow bags. I water every couple of days and fertilize every couple of weeks (have been using tomato-tone for the last few months). Located in Southern California, and temperatures have ranged from the low 70s to the high 80s (Fahrenheit) for the last few weeks. The blossom drop issue has been persistent for months. For a while I thought it was just too hot for them, but it has been consistently cooler for a while and it hasn’t improved.

The tomato varieties are sungold (1), super sweet 100 (1), brandywine (1), unknown large heirloom tomato (2), unknown heirloom cherry tomato (1), and black krim (2). The blossom drop issue is primarily affecting brandywine and the two unknown large heirlooms, I’ve only gotten a few tomatoes from them in total, despite abundant flowering. The small/cherry tomato varieties seem to be less affected, but they’re so productive in general that it’s less obvious when they’ve lost a bunch of flowers. It’s unclear whether the black krim have this problem, because I added them late and they just started flowering (they’ve each dropped a couple of blossoms so far).

I’ve had issues with spider mites, but I’ve generally held them at bay with diligent use of insecticides (spinosad and pyrethrins primarily). No other obvious disease or infestations, other than a potential fungus on my brandywine (I’ve removed damaged branches and started using copper fungicide).

Any thoughts?