If you feel the neck 2 inches above the bulb, at the place where the onions should be falling over, you will notice a thin spot if the onions are ready to go down. I think when moist weather prevails a lot of times they don't fall without help.

The other possibilty is the development of seed stalks (bolting). Once this happens the stiff stalk will not fall over on its own.

I have a few like that, but most have fallen over now [Candy). They are excellent again this year.

Do you grow from sets or from transplants? Did you change?

Shrivel? Have you watered them?