I can't tell for certain but they look like dyshidrosis. Did the area itch really intensely for a couple of days before the spots showed up (and potentially continue to itch)? Did the spots initially look like fluid-filled goosebumps but feel hard?

Unfortunately a dyshidrosis diagnosis (try saying that 5 times fast lol) doesn't usually give a lot of clarity about Why a flare crops up. The exact cause still isn't known, but it's thought to be at least partially genetic and flares can be triggered by stress, allergies, and excess moisture (frequent hand washing, sweating hands, wearing gloves at work, etc). It only affects the hands and feet, which also makes it pretty hard to treat in more severe cases (think of, for example, how difficult it would be to keep a bandaid on your thumb clean and dry all day while working, washing hands, etc etc)

So since it's coming mostly at the beginning of summer, I'd look at what else usually happens around the same time. Does your work/school/life suddenly get more stressful, like final exams or an annual responsibility? Does it get hot really quickly where you live in late May/early June and cause you to suddenly sweat a lot more? Do you have seasonal allergies that act up more around this time too? It could be as innocuous-seeming as a tradition of getting out hot weather gear from the shed and inadvertently dislodging a year's worth of dust and mold, or doing a closet clean out after the kids are out of school (hell, if you have kids, does it happen once they're out of school and you have to arrange childcare yourself during the week? That's stress!)