Whether you prune your own trees or have it done, you need to know good pruning from bad. The surest way to tell is by stubs. Stubs are bad. Also, a stub wound cannot close, and decay is almost sure to follow. As with most bad situations, the opposite is not always the cure.
Flush cutting is a no-no.
It removes the ring collar or ridge, at the branch base. The ring collar is the tree limb's natural foundation upon which wound closure is built. When pruning, do not remove the ring collar. Make your cuts nearly flush, but not quite. So, if your tree has stubs after pruning, or if it has been flush-cut, you are the problem.