Struggling to get high harmony in Breath Meditation

I’m having a hard time getting ‘high harmony’ with Muse Breath meditation. I’ve done over a dozen breath meditations and I can’t seem to get past 69% harmony, even though my breath is perfectly timed. Is it a sensor alignment problem?

Also, the background breathing audio track seems to disappear or start / stop randomly by a couple of seconds. What’s that about?

Please advise…