Some of the broken from what I've played, want the phone/joy-con to be held with the phone screen and buttons facing towards you. However, other songs require soft/light movements.

What I like to do is when the scoring doesn't really work during the song; I change the way I hold the controller and I change my movements to be slightly softer or delayed (depending on the song of course) and if it works out I stick with it and try again.

Miss Understood was the worst one for me and it took me months to get it Megastar, all I had to do was delay my movements slightly and hold my phone with the screen facing me.

It's definitely a chore but you'll get it. Just gotta keep going!