I sometimes want to automatically generate supports AND add my own, but it does not seem to work that way.
Either automatic supports OR manually made, not both at the same time.
Works for me, I just tested it out, automatically generated supports, and then added in my own structures, and when the G-Code was generated it included both supports structures. I'm using 2.2.2 on a Mac
When you're in the "Manually Define Support" dialog box, if you click "Apply based on overhang angle" it will put in the supports that would be generated automatically. You can then add or remove any support you want.