I’m assuming you mean the dance/action thing. The Pokémon do that every time they gain 50 points in the affection stat. There’s a maximum of 255 points, and the hearts increase at 1 point, 50 points, 100, points, 150 points, and 255 points. What’s happening is the Pokémon is doing the action thing for 200 points, but there’s no increase at that many points, so you won’t get any more hearts.
They also won’t do the action at 250 points. Probably because it’s so close to 255.
As for the items, you’ll get one when the Pokémon reaches 25, 50, 75, 100, 150, or 255 points.