This is just my theory, so take it with grain of salt
If not mistaken, gyno is tissue similar to the fat tissue. If that is the case, then you could reduce it but cannot get rid of it without surgery since once new fat cells are created, they do not go away they just get reduced in size. So unless one gets surgery, they will be prone for gyno since the tissue is there and will "fill up" again.
As for the AI, I have seen many arguments that AI only delays the gyno but not get rid of it. I believe I've read this argument posted by RRAdam and BigCat which would explain the rebound Caferacer had.