recording audio in midi backing tracks

I buy midi backing tracks to use in my duo and often record backing vocals on the tracks in LE6 and LE10. Most tracks I can just add an audio track and record no problems but some wont record any audio. I cant see any difference in settings on the tracks that wont record. Hoping someone can give me a clue on where to look. I use a scarlet 2i2 into a mac.

Hi and welcome,

Double.check the selected input and double-check the busses routing in the Studio > Audio Connections > Inputs, please.