It looks to me like it got too dry a week or so ago. I don't think it is a serious problem. Similar things happen when I wait too long to water my potted Japanese maples. At the time they are 'droopy' but recover turgidity quickly when I do water them and then a week or two later I have 'crispy' margins similar to what I see in your pic. In 'bonsai-ville' I will sometimes just remove the ugly leaves (cut through the individual petioles) when there is enough season left for a new flush. Otherwise, I just leave them on the tree until they fall off naturally. If you can definitely rule out something similar in your case, you should provide more the forum with more detail about the circumstances.