If you are looking at this post, I believe you found that your S8/S8+ having some odd behavior which it gives you notification when your screen turned off.
This is the 1st time I get a Samsung Galaxy S8+ phone. It seems like due to the Galaxy Note 7 issue they trying not to give the phone bigger capacity. So when Samsung S8 got a small capacity battery and want to cope up with nowadays competitors? They implemented battery optimization by default, without giving the user know. Which is they actually turn off your app sync function when your phone going to sleep mode/screen off.
So if you want to get it fixed and don't want to miss important message, follow below steps.
1: go into settings, search for "apps" and click into it.
2: once inside "apps," hit the three dots on the upper right corner, go into "special access."
3: once inside special access, go to "optimize battery usage."
4: from here, tap on the dropdown menu saying that says "apps not optimized" and switch to "all apps."
5: once all your phone's apps are shown, find the apps you want to receive notifications as they come through, and tap on the switch to turn it off.
This is the most hilarious agenda you have SAMSUNG !! There is no heads up on this issue to the user at all. You have to turn off the switch by yourself to ensure the phone doesn't automatically kill your app, so you can get notifications on time.
