I have acers planted both in the garden and in pots. Over the last year 2 dissectums have started to die. Both were planted about 7 years ago and have grown to over 6 feet. The main branches start to turn black and this progresses up the branches to the stems. Cutting back the branches has not stopped the problems spreading to other branches. So far a red branched acer within 2 yards of the 2 affected trees is not affected. All are mulched with eiricacous compost and watered equally during dry spells. I attach a photo of one of the remaining branches.
The photograph shows a problem called die-back, which is common with Japanese maples when conditions of soil or exposure are not ideal. Overly wet ground is the usual cause and mulching heavy ground can make it too wet. Plants in pots can suffer root restriction after a few years and die back if not potted on.