What’s wrong with my mango tree?

sisi starts with ...
I am hoping someone can help diagnose what could be wrong with my mango tree.

Over the last 3 months we have gradually had a large increase in dropped leaves (spring-summer) here in Australia. Someone of the leaves dropped appear healthy, other ones have discolored spots whereas others are just light brown. It started where one side of the tree seemed affected whereas now the whole tree seems affected.

There is a stag horn on the tree which is quite large and half of that appears discolored now too.

I pruned back many branches which were dead about a month ago in an attempt to save the tree, it it appears to not have worked at all.

Do any of the experts in this forum have any idea?

Pictures - Click to enlarge
Picture: 1

sisi says...
Here’s a few more photos. Hopefully they will help diagnose the issue?

As a futher bit of background, all flower beds nearby have cypress mulch and are doing really well at the moment.

The neighbour installed his shed along with lots of earthworks about 2 years ago. I expected that a lot of the roots were cut on his side of the fence but the tree has only starting looking particularly bad the past few months so this may not have affected it.

Fingers crossed someone you can help because I really like the tree.

Pictures - Click to enlarge
Picture: 1	Picture: 2	Picture: 3