When playing Yousician on devices running Android 6.0 (Marshmallow), please make sure the app is able to access device microphone.
If Yousician is not able to access the mic upon launch you will see a pop up suggesting to "Allow Yousician to record audio".
You can either enable the mic access by tapping "ALLOW" or by going to the app properties on your device and enabling microphone access for Yousician:
Settings --> Apps --> Yousician --> Permissions --> Microphone.
If the mic is not enabled the following screen will be shown before every song: