You said yours have never been hot? That's why I said "sometimes hot". Obviously, others have had the ones that are hot! . Some time ago, in my quest for a varroa resistant bee, I researched every bit of info I could on beeweaver, the methods stated on their web site, and further information from other commercial beeks including a commercial queen breeder, who have had dealings with them.
I'll admit this was an academic excersize, as I am overseas and my country will not allow bees to be imported. But I wanted to see what I could learn that might be useful to me.