I don't normally have any problems with clearer boards, but this year I did. The bees in 2 hives did not descend as they are supposed to do and the supers were full of bees after the clearer boards had been on for 24 hrs and still after 48 hrs. There's no brood in the supers btw. A couple of the hives where the clearer boards worked had 30-40 dead bees on top of the clearer board when I lifted the supers. I don't remember this happening in previous years.
I guess the cold overnight temperatures might explain the dead bees over the clearer, but should have helped persuade the bees to move down In the hives where the clearers didn't work.