Help!! It’s chipping!

So I’ve been making yard art for a few years, and I’ve made numerous things.

I usually work with plywood (that’s thin similar to paneling) and it’s never chipped. I always clear coat it with polyurethane.

Someone had me paint this huge pallet and she’s had it for a few months. It was for outdoor decoration. She just messaged me and told me it’s chipped really bad 😥😥😥 the other stuff I’ve made has never done that, like at all. And it’s been through several thunder storms and snow for two years. No chips.

Is it the pallet wood? I’m super stressed out.