Maybe onions just don’t like clay even if it has a nice spot dug out and replaced with better “soil”? I’ve tried several types of garden soil and potting soil. Maybe I just made a big fancy / too often from rain soggy bucket in the ground. The tomatoes like it though. At least there is that. :-)
Wild onions seem to have no problem. Figures.
We have zero clay but I think there is a way to break that up. Lime? IDK. Adding sand for an onion bed should work.