Blocked Entrance with dead bees

[Etton]

All hives active, bar one. Imagined they must have died but upon opening loads of bees in the top box but the varroa board was chocca with dead bees. I do check regularly the entrance is clear and remove one or two dead ones but even with looking under the varroa board it’s tricky to see. I removed the nadired box and loads flew out, presumably to go for a pee!