I did see something that I don't understand! On three of the frames there were capped brood but the cap had a small hole in it. There were also cells that had bees in them that looked as if they were fully developed but were dead.
How much you hive has room? If it is too much, it not able to keep brood area warm or it is not able to protect it.
3 frames brood is a good colony. Of course it must protect it against it's enemies. Noboby else can do that.
At autumn when winter is coming bees let brood die and carry them out. Could it be that? It is usual that one day they carry all out even if brood is almost bees.
If varroa contamination is big enought bees carry out wingless emerged bees. Varroa does not cause winless, but it is a virus.
Small hole may mean that bees have started to take away brood. They first open the cap.
But dead brood in 3 frames is quite much.
Difficult to say from long distance...
In American foulbrood there is tiny holes through caps. Then you may have 3 frames dead with small holes. If you look inside, do you have coffee brown tar inside cell.