Holes in cherry tree leaves, and leaves only at the end of branches

I'm trying to grow a Stella cherry tree with a Gisela 65 rootstock in a container on my balcony.

Last year most leaves developed holes pretty much as soon as they appeared in April/May, then the leaves curled up around June, and fell off in July. Although oddly enough the ends of the branches sprouted new leaves in autumn, as though it thought it was spring, before winter came and killed those leaves.

I had thought the holes were caused by slugs, and was catching 30-40 a day on my small balcony at the peak last year, and that the leaf drop was a result of this damage. However, this year, despite regular checking, I've only found a small number of slugs, so I'm not convinced that is the cause any more. I can't see any evidence of any other insects, and the holes don't appear to have been preceded by coloured spots or other symptoms which might indicate disease. Many of the holes are very small and in the middle of the leaves, although some are larger and around the edges, so it is possible there are a couple of causes. Searching online, one theory may be wind damage because the balcony is on the top floor, but I'm not convinced about that idea.

As for the issue with the leaves only at the end of branches (which wasn't an issue last year), I'm wondering if this is a leftover from the issues last year, specifically new leaves appearing in autumn and being killed off over winter. If so, I'm hoping that it'll get back to normal next year, asssuming the same thing doesn't happen again this year, but again I'm not sure.

Anyone have any thoughts? And/or any other tips for trying to grow a cherry tree on a balcony?