Catalpa bignonioides

Just looking at my lovely tree which is now three years old and 3 M in height and found several serious ares of wilt and die back. RHS pages say the tree is basically disease free but something is causing severe damage.

Hope you can see from the photo, the stems have been killed in the length of the branch and totally destroyed . growth is sound below damage area and was above until  it rotted through. We have gad nothing abnormal weather wise, no extended draught or late frosts , no signs or aphids or other insect life , no physical damage except a bit of high wind which was not gale force.

I am puzzled , any thoughts would be appreciated.