I think your tree is beginning to show signs of Verticillium Wilt. It's a
virus that nursery raised maples seem to be prone to. I had one in a pot
that had leaves showing the same symptoms as yours and pruned and babied it

Um, verticillium wilt is a fungal (not viral) disease caused by
the fungi Verticillium albo-atrum and V. dahliae. It does cause
various symptoms in a number of woody plants, including true maples,
the genus Acer.

However, "flowering maple" is not a maple at all, but a member of the
hibiscus-cotton-okra family: the scientific name is Abutilon x hybridum,
although related species like A. megapotamicum and A. pictum are also
called flowering maple..

My WAG, based on the photo and descriptions, is that there may, indeed,
be a viral infection of the plant. Have you submitted a sample to your
extension service for diagnosis? The diseases I've seen most commonly in
Abutilon have been Rhizoctonia root rot and Rizoctonia web blight, but
the symptoms don't match.