How do I consistently receive notifications from one app, and no others? This basic question has become increasingly difficult over the past two years. 

I have a Samsung with Android 8.0. Amazing, I cannot rely on Calendar to make a tone before an event, and this state of affairs has existed for two phones (S7, S8). The layers of control I see:


Under "Notifications" in Settings everything is off but Calendar.
There is a do not disturb function which has a toggle to allow calendar 
events at all times. That is on.
"Easy Mute" a samsung feature, is off.
In Accessibility "mute all sounds" is off.
I make sure calendar events have a notification, as is the default.


However, the notifications still intermittently fail to make a sound, although popups seem to always happen. They are especially likely to fail in the morning. There is a separate "notifications" volume, affected by some of the previous, but not others, which often (but not always) shows off when the issue occurs. The same problem has followed me through two phones (s7, s8). I have reset my entire phone in an attempt to get this working, but the issue remains. I have changed Google accounts in an attempt. No luck.

So, how can I consistently get my calendar audio notifications?
I had what seems like this problem in reverse i.e. I was getting notifications from too many apps. After searching for any and every possibility I could think of, it finally turned out to be with Google and Facebook settings for my problem.

If it has been 2 years and no joy, you have most likely tried all the suggested places to look below but if not I hope one of them helps lead you to the answer.

Regarding Calendar notifications with Google here is a link to the page on Google Calendar Help that might help: https://support.google.com/calendar/answer/37242?co=GENIE.Platform%3DAndroid&amp;hl=en

This will take to a YouTube video for the Galaxy S7 on the Android side but not specific to the Calendar: https://youtu.be/Z0ZeJdRPTWk

Here is another link to a short article on changing notification sounds to help isolate it: https://www.greenbot.com/article/2688096/how-to-change-notification-sounds-on-your-android-phone.html

Third party apps such as "Greenify" that hibernate apps you have specified when the screen goes off would also keep notifications from getting through. Here are a few more links.

S7 Notification Reminder: https://youtu.be/tiEwnht-JWg

S8 Calendar Notification: https://youtu.be/hETYdfgK45Y

This worked for several users: Go to settings, applications, application manager, then message. If notifications is set to block. Unblock it.

Lastly the best resource I have found for Android phones is at XDA-Developers: https://www.xda-developers.com/ It is definitely worth searching the site for your exact model of phone. 

This is where I learned how to root Android phones. I found that the number of variations in the same phone is mind boggling. The exact model number &amp; where a specific model of phone was made could mean the difference between groups of people having the same problem while others do not.