hawthorne leaf issue

[ABCarve]

I have a native collected hawthorne, so I don't know the particular variety. Some leaves have developed this curl. I open up a leaf to see if there is some critter in there, but nothing I can see with my eyes. So.....animal, mineral, insect or bacillus? It doesn't seem to be hurting the tree although it can't be helping it.
Does anyone have ideas.