Unable to change my App Notification Tones

I am unable to change my App Notification tones for my devices.I have gone into:- Notification settings- App Notification Tones- Selected a tone: message comes up with **‘your sound could not be loaded’**- I am unable to adjust the volume as wellI have logged out of my phone,I have logged out of my account.I have put my account onto another phoneAnd it still does not allow me to change my tone for any of my devicesAny help to rectify this would be appreciated as it is stuck on silent which defeats the purpose of having the notification app. It worked fine for the past year until yesterday