Have you had any hail in the past month or so?

No, and I was really hoping someone on this forum could help me.

Would prefer to see an overall shot of the entire tree to confirm but that looks like the result of uneven watering. JM's will frequently develop random spotting on their foliage that will eventually dry and sometimes fall off if their watering has been uneven. This is most common in containered trees; almost nonexistent to those established in the ground.

Uneven means allowing the soil to dry a bit much between waterings then soaking thoroughly when you do water. Better to keep the soil just consistently moist.

Aphids Japanese beetles

Aphids do not make those sorts of leaf markings. They are sucking insects so no holes or brown, dead patches and their presence is indicated by leaf deformation or distortion...of which there is no sign. Also, if Japanese beetles were to blame, there would be large parts of the leaf missing or skeletonized.

As someone who has grown, sold and collects a wide array of JM's, I can state with some assurance the leaf markings in the OP's photo indicates just a watering issue.....nothing any more sinister than that.