In a recent update in Sonos, the Sonos API only works with custom room names and not the Sonos default names. As such, if your voice notifications/doorbels have suddenly stoppped working. Please follow the steps below and create a custome room name. For example, if your notifcations for room name "Kitchen" stopped working, as "Kitchen" is a default name in Sonos, create a new room names called "Kitchen Open Plan" for example.
Open the Sonos app and tap the settings wheel at the bottom right.
Open System.
Select the speaker you want to edit.
Under the Room section, tap Room Name.
Enter your new name and tap Done.
See below screenshots on how to do this.