Walnut tree - bark problem on my beautiful walnut tree

Hello _ I have a lovely walnut tree which produced its first nuts last year. About 4 or 5 years ago every leaf on the tree turned black and I pollarded the tree back to the trunk. The tree seemed to recover nicely and put on 4M of growth however is now suffering from significant bark loss on major branches. Can anybody help or advise ?
Many thanks !

 

I assume that the branches with the bark loss are either dead or possibly dying.
Wouldn't like to guess why.

 

Looks like bacterial canker. Have you noticed any weeping or exudates from the bark at all?