Certified GKH Gardening Expert
How old is the tree? How long has it been in the same pot? It may need its roots pruned or need to be repotted in a larger container. It could have a pest.
Here is a link to several articles - check your tree's growing conditions, inspect it carefully, and hopefully you'll find your answer here: https://www.gardeningknowhow.com/ornamental/trees/japanese-maple/japanese-maple-problems.htm