Not wishing to sound too harsh but I will stick with my original diagnosis of inadequate varroa control. If I may quote one of your earlier posts from a few years ago:-
"Firstly i would like to thank everyone for their help and opinions.
Because everyone bee keeps differently and there is no set rule on what is right and what is wrong, and the only one who knows best are the bees. I think is it wrong for people to say that you should never do this or never to that?
The guy who taught me beekeeping has used sugar dusting for years and we both think it is a nicer way of treating the bees then using chemicals. He has been a honey farmer for years and has over three hundred hives. He has not seen any evidence of lack of emerging brood or any other side effects. I also know a beekeeper who dusts his bees with dust from the roads and paths?
(The way I look at it is I would not like having chemicals put in my house or put all over me).
I have two hives and two nuc's on the go and the varroa count is very, very low.
All I am saying is this is what works for my bees."
I rest my case.