Spadge Vernacular
Player Valuation: £70m
Inspect the roots it may have the deadly pest vine weevil grub that eats the roots they are the size of a small prawn if they are present squeeze them dead get a good root ball prune the acer by a third and repot the plant .....
I am guessing that is the problem .......or it has root rot if you have overwatered it if so same treatment.....
Look at the leaves if the ends have a chunk out of them the adult vine weevil has hosted on your acer it's larvae will eat the roots look for 3-6 or more larvae prawn coloured grubs they munch through roots causing the wilt, and if left will kill your Acer .....
Our Acer is looking a bit distressed so, remembering this post I went to give it a look over. As I looked I spotted two beetle looking creatures, the larger one being as you described, looking like a tank but when I looked at the smaller one I couldn't help but think 'that is the lesser of two weevils'.