Q.Leaves falling off japanese maple (crimson queen)
Leaves are falling off the upper part of the tree. Leaves started growing back in bright red color and then stopped growing. The bottom part of the tree looks good. The weather has been very hot all summer.
Your tree may be dropping leaves to protect itself from the heat and dry conditions.
I would give your tree some additional water during the dry period.
Here is a link to refresh you on the care requirements.