Two sets of pumpkin plants, one dying and one thriving

I'm trying to figure out the difference that is making one set of plants thrive and another die.

I have two areas of dry garden, one under deep leaves and one under deep woodchips. Both are planted with pumpkins. Essentially the same soil, sand and rock. I should think that the leaves and woodchips would provide the same soil protection. Underneath appears to have about the same amount of soil moisture. UV has been insanely high, ranging 10-12 most days. I assumed that's what's happening, but I should think that would affect both sets of plants.

Under leaves: In front of the greenhouse. I caved last week and started watering because the plants looked dead. It didn't help. Completely wilted by 11 AM, but usually back by morning. One failed to recover. The more "normal" time for wilting is 3-4 PM. They get pretty much full sun from 9 AM. I have seen one squash bug nymph and a few eggs, but no adults.

Under woodchips: In the parkstrips, between road and sidewalk. Not watered (by me) all season and still look great. Full afternoon sun, dappled morning shade, but just starting to bloom. No wilting visible at 7 PM.

Any ideas as to why these are behaving so differently?

You are clearly a master gardener compared to me.  I have planted pumpkins 5x this year. None have sprouted ....everything else is doing good.

I think I figured it out. As the plants started to deteriorate I could see soil through the leaves. Obviously the leaves break down too quickly. I'd been testing the soil moisture around the edges of the bed, where leaves were still quite thick. I've put up shade cloth and watered the plants and blossoms are already popping out, the leaves returning. While the UV was definitely part of the problem, the water didn't help. So I have watered twice this week, and I'll water again in two weeks.

If this is going to be a dry garden area I'll need to cover it in woodchips rather than leaves. Still, I have three plants that survived both high UV and no water for three months, so that's something.