Based on a previous post you made I'm guessing this is a question about ACL 16. Is this correct?
You say you have recorded the same track in the past but now [it] omits some instrumentation. Taken literally at face-value I have to say that is impossible! The app will either record all the audio it receives, or none. It cannot select "some" of it to record and simultaneously discard other sounds occurring at the same time!
So, please, a little more detailed information about the problem and about your computer.