Instruments bugged?

Is anyone else having trouble getting instruments to sync? Specifically the guitar and flute. I know they’re supposed to lock in together, but I’ve had multiple runs where they just don't sync up at all and play over each other.

Also, are you actually supposed to be able to play two guitars together? I know for a fact you can do double flutes, but I can't get it working with guitars. Not sure if that's intended or just another bug.