My escallonia hedge which i have for 20 years has lost its leaves over past three to six months, never seen this before, always a good thick hedge all year. All in my area with a similar hedge have the same problem. I believe its a leaf spot disease, if it comes back to life in spring will the same happen next autumn is it going to be a ongoing problem, we had wet summers before and i did not see this happen?
It is also possible that cold weather, exceptionally cold in recent weeks, has caused further leaf loss as escallonia is not completely hardy.
It will re-sprout but leaf spot is likely to be a problem in a wet year for the future.