mine came from ca. i have the same problem. very gentle up until a couple of weeks ago.
i think it's robbing, heat, honey, and no flow.
smoke made them mad as heck, but a i turned the top cover over next to the hive, and sprayed the inside with some sugar water. they all jumped on that and left me alone (kind of). figured if it was on the inside of the top cover, it would go back into the hive and not encourage robbers. i also used a little light spray on the top of the heaviest frames and that helped too.
don't know if that's the recommended course of action, but i was a little desperate!