ZTE Quest 5 phone keeps resetting to "vibrate"

[Roger Blair]

I have a ZTE Quest 5 phone. Whenever I set it to "non-vibrate" (so I can hear it ring), the phone later resets itself to "vibrate.: How do I stop this? (Note: I don't think it's operator error, since I don't use the "settings app very often--mostly to turn "vibrate" off.)

 

[B. Diddy]

Is Do Not Disturb scheduled to turn on? Or could it be that the Volume Down button is being pressed and held inadvertently?