This disease seems to have only just got here but some of my ashes have had a problem for several years. In the middle of summer a lot of leaves fall off with no warning. One day a normal looking tree, next day the surrounding ground is covered in leaves, this continues for a week or so. No tree has died completely but branches have died back and eventually fall or are cut off.
The first tree to suffer, at least 8 years ago, now looks fine with no recurrence.