You might have a problem with wireworms in the soil. I get them in some hills of melons that I plant.

So this year I cut a few potatoes into pieces about golf ball size, speared them with a pointy stick and put them about 4 or 5 inches into the ground, with part of the stick staying above ground. Then after a couple of days, I dug up the stick+potato. If it has the little orange half-inch long worms poking out of it, then they are likely the problem.

Around my watermelon plants I had a "nest". I stopped counting after killing 30 one day.

Put more potatoes around the melon plants and the wireworms will go to the potatoes. Dig up the potatoes every few days and kill the worms. Replace the potatoes and repeat.

I only did it that once with the melons, but am trying to get rid of them in another raised bed where I couldn't get peas to germinate this year (after 4 tries!) yet they germinated really well last year.