Definitely should not be losing leaves in summer. If you can, I'd turn it on its side and slide it out of the pot a bit to see what's happening.
Sometimes potting mix dries out too much in the middle, and then is hard to get wet again. It will appear to be moist on the top, but the whole pot is a dry brick inside. The water you give it may be running right through but not getting to the roots.
IF you find this, you need to stand that puppy in a deep pan or bucket of water, or break up the dried soil a bit, then soak it.
