After upgrading to Android 10 the Do Not Disturb setting right away stopped working 100%: during the night it (once?) makes a notification sound ("dingdong"), which is exactly what you don't want. The same sound is also heard when switching Do Not Disturb on (from the top of the screen pull-down menu), which is new too. The "dingdong" is set as the notification sound for my SIM. I have only 1 SIM installed. As exceptions I have/had "Alarms" and "Favourite contacts". This worked fine in Android 9.
I've been through all menu's, settings, forums etc. but cannot find an answer.
Hey @JVQ! Can you confirm what type of notifications this is? Is it for an alarm, a notification for a third party app or something else?
If I only knew.... that is the problem.
My S9 began chiming when my Do Not Disturb is set to turn on. It goes on at 10pm and after the update my phone alerts a sound like messenger when it enables at 10pm. Annoying.
This exact issue is happening to me. There is no way to turn off notification sounds while do not disturb is on. Of anyone has figured it out please let me know.