Lately I've found myself having lots of trouble with fast singles that happen to be going in a similar direction. It's kind of hard to explain, like a really spaced out stream, if you've ever played the Insane level of Kokou no sensei, you probably know exactly what I'm talking about. Anyways, it's usually only those types of fast singles I have a ton of trouble with, I can usually get through squares and other shapes with ease, but I always move through these too fast/don't hit the button in the right rhythm.