Prune Tree Disease?
As I ment5ioned on Facebook your images and description are not enough to begin to answer the question. A little more information please.
Do these images help? One abnormal thing that happens is about 2/3 of the tree gets extremely thick (brush like). The other 1/3 of the tree is the only part that produced fruit this year. The tree bark seems normal. Please provide guidance on what other kind of information I can give you. Thank you!
A whole tree shot might be best as all your images are much too close. You hinted a little more about the problem. A thick bushy appearance may mean you have a whitches broom. Lots of shorter shoots with shorter internodes. Look at the images cherry and see if they fit:
Then see if the description for plum pockets fits: