Hey B. Diddy - Similar to the OP my Samsung S6 Edge has completely stopped making "default notification sounds". I went all throughout my sound settings and my ringtone is still working fine... The weird thing is, even when I go to change the notification by selecting another sound that chime doesn't even make a sound now... I'm used to Notification sounds making their sound when you select any of them as a preview.
I've restarted my cell several times over the last day and double checked that everyone on it is as up to date as possible.
Thanks for any advice!