Something is wrong for certain and it's probably a root fungus. The tree though not dead is diseased and can be removed if that is your choice. Once removed do not plant anything in its place for a few years since the soil is most likely contaminated with whatever infected it.

Well clearly its not dead because it did this last year but still put out leaves this year. Can you post a photograph and answer a couple of questions:

How long have you had this tree?

Can you inspect it from top to bottom and side to side, checking all branches, the trunk right down to the base, and stems for any sign of something that shouldn't be there please (such as soft spots, weep stains, insects, fungus)?

Mabye this is the natural cycle of the tree
Because the same happened last year,it could be something to do with the environment...
how often do you water/feed/prune the tree?
Maybe check if its damaged anywhere?

Our red leaved crab is an old tree, it doesn't like hot dry conditions and like now has an early autumn, as its a wet day it could stop going brown, just conserving energy I think....

Many thanks for useful info