Lock screen and keyboard sounds have quit working. The settings are correct and the device is not muted. What else can I do to get the sounds working again?

Four days ago the lock screen and keyboard sounds quit working, but was able to reset the settings. Two days ago I had to do this and turn off the device and then restart it to get the sounds back. Today they suddenly went out and I can't get them working again. The settings are correct and the device is not muted. My OS is up to date. What else can I do to get the sound back?