Heart rate monitor and built-in sleep tracking

Is it possible to have a heart rate monitor active, while still having Sonar or Accelerometer set as your sleep tracking sensor?

I have a mi band 2, and even after checking Wearables > Heart rate monitoring, I don’t get heart rate info, unless I also check Wearables > Sleep tracking. But if I select that second option, it seems to ignore input from sonar and accelerometer, and I get a flat reading for the whole night, except for heart rate.

This looks like there’s some trouble reading the accelerometer data from the Miband.
You should get both accelerometric and HR data from the Mi Band.
Could you please install the latest beta version from https://sleep.urbandroid.org/wp-content/uploads/release/sleep-20180818-beta-release.apk and try with that?