If the tracks don't place it's most likely because you're dropping them on your partner's turn instead of yours. Unless therr is some kind of other bug. This isn't your fault, it's mine for not making the game communicate this idea strongly enough or giving you feedback when a piece fails to be placed.
As player one the light green area is yours and the dark green is your partner's. You can only place track on the beat of the music when a light green areas is next after the existing track. Sorry for the confusion.