Any Japanese Maple doctors in the house?

[Muushka]

Hi. I don't usually visit here, but was hoping someone could give some advice.

I have several Japanese Maples. 2 pretty mature ones about 20 feet apart. They are each about 15 years old.

One of them, which has grown like a week is suddenly not doing well.

Shedding leaves, arbitrarily. Several branches are bare now, so sad. The other one is perfectly healthy.
Nothing has changed in the area at all.

I tried to inquire about it at our landscaping place but they insisted on a house call
(I did bring a branch and could have brought pictures).

Has anyone got info to help my poor tree? Thanks