For almost any animals, they need to be near optimal first, or at least doing well, before they can normally spawn and sexually reproduce. One obvious exception is the "last ditch" spawn where an animal spawn right before they died.
IMO, Genicanthus are larger planktavores that needed open water, larger tanks with clean water and a lot of water movement. Most important thing that is lacking in most tank is the manner we feed our fish. Our tank are very lacking in food that suspended in the water column in comparison to the wild. IMO, a lot of the Genicanthus angels we keep will not sexually mature becasue we cannot provide the optimal condition for them. From my experienced, they are very active fish that is wide ranging in their swimming habit. Like many active planktavores, they require continuous food intake. I feed my tank a lot, I don’t see them have a bulging stomach, with food like some of my the other large fish.
Those of us that have a large tank, and feed a lot appropriate food in small amount each time will have much better success in keeping a thriving Gennicanthus angel, and have them sexually mature and spawn in our tank.