My Kabocha plants were doing fine and started setting fruits:

But recently somehow the plants are wilting during the day and recover at night. The weather has been on the cool side (65 to 82F) and the soil has been wet from the heavy rain a week ago.

Since the plants are not lacking water, I do not know what is going on. The leaves do not have holes and I do not see any obvious bugs. The plants are somehow close and I do not know if that is the cause.

Is temperature too low?
Too much water?
The soil was newly dug previous farm land.
The soil lacking something?