Same thing happened to me a couple of years ago; fertilized just before fruiting and some trees just after. Worst year ever, and fruit all dropped. Not a coincidence, and has been validated by others.
Do not fert when flowering or fruiting unless you know what you are doing or are okay with experimenting. Fert usually should be done well before flowering from what I can tell.
Keeping it simple with my workhorses, and things are back on track. Going to experiment more with foliar feeding and micros during flowering and fruiting, but not on trees I am depending on. Much to learn have I