Notifications Volume Low Issue's Possible Cause.
Some are finding volume notifications too low after getting new update of 10.3.1 and it might be caused by this, Go to 'System Settings' > 'Main Volume' > 'Always Adjust Media Volume' (Make sure it is turned ON)
If 'Always Adjust Media Volume' is turned off, every time you lower the volume when playing music for example, it will also lower the Notifications volume until one or the other is increased.
Then go to 'Notifications' and slide Active profile sound bar all the way to the right. And set to Normal.