Once the onion tops have died and the bulbs are just sitting there, you don't want them to start rotting.
Are they getting
water on them from any source? Is the sun baking them and softening them in any way?
I try to get mine out of the ground and into a cool dry location as soon as the tops are dead and dried, as they tend to start to rot. Rotten onions STINK to high heaven when you try to store them.
"The rule of no realm is mine. But all worthy things that are in peril as the world now stands, these are my care. And for my part, I shall not wholly fail in my task if anything that passes through this night can still grow fairer or bear fruit and flower again in days to come. For I too am a steward. Did you not know?" Gandolf