Update - the kind and knowledgeable people at Penn State Extension identified the problem as a fungal disease and advised to have them replaced.

This is what they wrote

”The tree is suffering from a fungal disease, probably apple scab, and will loose the damaged leaves, leaving the tree unable to make food. While a mature tree can withstand a certain amount of leaf loss, young trees have not yet built up a reserve to see them through stressful times.”

Funny that an Extension office wouldn't be more specific. Anyway maybe the previous scab resistance of 'Prairifire' has been overcome by new strains. Or there were strains around from the beginning that could infest it, in some areas. Such details are critical to whether or not a planting will be an attraction or a headache, for those who don't want to spray.

Funny that an extension service would not be more precise. And that damage really doesn't look very much like scab (which Prairiefire is supposedly highly resistant to).

I also have to wonder about a university that would confuse 'loose' with 'lose' :-) It's a small point but would indicate that maybe the response was not generated by a trained pathologist but rather just a volunteer, who perhaps has not had all the training necessary to be able to accurately diagnose diseases.

You could be right. This is where I sent the pictures. https://ask.extension.org/ask

In their defense, I thought the trees were prairie fire, but maybe a different variety was planted, so they only had my word to go on.