lost a hive in two days

what did the brood look like?

Did you notice any fighting, or robbing activity? Where there dead bees on the ground in front of the hive?
That would be my first guess.

I would suspect a "P" kill as my first guess. Robbing wouldn't kill a hive like that.

Everything on the frames looked fairly normal. I thought pesticide also, but there are 5 more hives there and they're okay. The hive died in the bottom brood box, they'd fallen to block the entrance and spilled out onto the landing board and were out in front. When I checked them a week ago, they were doing okay. This happened FAST! I'm puzzled as is my mentor.

Are the frames oily like SHB? Is the brood white or diseased? Does the hive smell bad? SHB is the fastest and most prolific killer in Florida this year.

It's been rain for a week here

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Have you ruled out starvation? what was the level of stores like?
Another possibility is suffocation due to a blocked entrance.

AmericasBeekeeper said:

SHB is the fastest and most prolific killer in Florida this year.

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In my experience, shb don't kill bees but will drive them to abscond.
In my opinion, starvation or pesticide. It is possible that this colony found a contaminated nectar source that the others didn't....although it doesn't seem likely that none of the others would have any symptoms.
Starvation sounds plausible.

SHB - Don't think so.. no smell, normal looking frames, brood looked normal - but will research.
Pesticide: possible It's a very agricultural area although my neighbor will tell me if he has to spray and that generally occurs later in the summer.
Starvation: I did feed them until the apple trees bloomed and they quit taking syrup. I had put on a second brood box. I can't say what the food supply was when the rain came.
Suffocation: might have taken a few out, but what killed so many as to block teh entrance?

Thanks for the insight - much appreciated.

Were the dead bees wet? If you had rainwater leaking inside the hive and soaking the cluster, that could wipe them out in a hurry.

No.. a new telescoping cover and inner cover. With all the rain, that was a definite possibility had it not been good equipment. And the bees were dry. With no food, I'm sure guessing they starved, but hard to believe this time of year.

I think they starved. I had 1 hive out of 16 that were kicking drones out so I checked right away and found they had no stores, 8 days ago they were ok. Like with you it has rained every day for over a week here and the bees haven't been foraging much at all. I put a feeder on that hive right away and now need some sunshine.