There is more than possibility. It could be water & heat stress if the water is not reaching the roots. I have been having to babysit my shrubs and trees more than usual due to excessive heat and drought conditions in my area. I am not a tree expert, however. If it is a pest, you should see signs of it. There are some sycamore specific pests. But your doesn't look like a pest problem. The leaf scorch could be from powdery mildew, which thrives in shady humid conditions. That would require a pesticide. But it's hard to say. You should be able to find lots of information online. Sorry I can't help you more.
ISFP "The Artist"