Someone asked about this phenomenon in a MN vegetable
gardening group on
Facebook and the consensus seemed to be that it happens on especially windy years. (I didn't look it up to figure out if this is really that, but that was their claim.) And folks were divided on whether to leave them be.
In my case, I inspected my flopped over bed and saw that they were drying at the tips and necks, and there was some black moldy stuff forming, so I lifted that bed. (And this may be entirely aside, or may be part of the same regional weather phenomenon, but my potato onions in this bed failed to produce flowers entirely, but formed nests better than the previous two years I've been growing them.)