The Kwanzan Cherry tree in your picture does not show much about the tree except the overall shape and location of the tree.  These trees are not long lived and are subject to several diseases and pest problems. If you could take pictures of the leaves close up that seem to be affected( both sides of them), and also pictures of the trunk. Look for any cracks in the bark or small critters on the leaves. You can take a small branch and tap it against a sheet of white paper looking then for black specks that may move. I am including here some links to problems with Kwanzan Cherry trees that you may find useful. There are some reasons for yellowing and leaf drop on most trees, but if you have not seen this before it warrants more investigation.
You may also wish to do a soil test of the soil under the drip line of the tree and information of that is in the following link:

https://durham.ces.ncsu.edu/2020/05/nows-the-perfect-time-to-test-your-soil/

The following link takes you to the Extension Tool Box, and if you scroll down, you will see that this tree is prone to several insect and pestproblems.https://plants.ces.ncsu.edu/plants/prunus-kanzan/

With more complete pictures we may be able to address your questions with more detail and diagnosis.  You are also welcome to bring in a branch for evaluation by our agent who will return next week. Our address is 721 Foster St in Durham, hours are from 8am-5pm, M-F.
https://ask2.extension.org/kb/faq.php?id=337276
https://ask2.extension.org/kb/faq.php?id=479996

It looks like a fungal infection called brown rot. The homeowner reports that "The leaves are now brown BUT are soft to the touch. As stated in previous emails, the tree has been fertilized, treated for fungus and pest and is on a watering schedule."
The fungal disease may have returned.
My resource: https://extension.umd.edu/resource/brown-rot-ornamental-cherry-trees

Tina

Durham County Extension Master Gardener