Is that pale area a long snag? Acers do tend to get a bit of dieback and if you leave snags they can cause disease to spread into the living wood. I think I'd be removing the whole branch to make sure no diseased wood remains, and maybe spray with an anti-fungal (I use garlic wonder as an anti-fungal and it works well)
@icedance the bad leaves are on the branch that ends with this white part and black ring. It's in ericaceous soil and been in a couple of years, this year is first its flowered . I've been too dressing with fresh acidic soil and then feeding in spring with ericaceous food
All good so far .. I would be cautious about cutting back all the way as the area does spread into the main stem .. we can rule a couple of things off the list if you can cut back half way and check within the stem .. if there is a dark brown ring within or black, or if you peel back the bark you have cut off are there any brown streaks ?