Planted in a spot where it is windy and/or lack of water. Unless you are i an area of alkaline soil and are not feeding with ericaceous compost.

Have you by any chance done one of these,
(1) watered feed over the leaves ?
(2) Used a watering can thats had the likes of jay's fluid in it and its not been rinsed out 100%,?

Just a few thoughts that may cause the leaves to bleach.

It looks like Rust disease, but I have never come across it on acers. If you have a gardening book look up diseases it may help. Otherwise as, Moon growe says, give it a drenching with added feed.

Many thanks for your advise. I'm sure I've not used a watering can with Jeyes.