If there is a live photo wallpaper on the lock screen and the user uses 3D Touch to view it, then from then on the music volume will be used instead of the ringer volume for all notifications. Also if the "control with buttons" option is enabled, the volume buttons will change the music playback volume instead of the ringer volume.
To get out of this state either turn phone off and on or replace live photo wallpaper with a still photo one.
This one really annoyed me until I figured out the cause and work around.
To get out of this state either turn phone off and on or replace live photo wallpaper with a still photo one.
This one really annoyed me until I figured out the cause and work around.