I wanted extra notification sounds in my android 5 device (Micromax Canvas Tab P290). After rooting, I added some ogg files to
/system/media/audio/. For unknown reason, all the notification sounds are missing from the apps. The notification sound list is empty. I have been careful about the permissions. All permissions are
755 for directories and
644 for files.
Also worth noting is that screen lock sound and touch sounds work. Alarms (from the stock Clock app), notification tones from apps (WhatsApp, Hike or similar apps) do not list any sound files.