[Samsung Galaxy S8 Questions and Answers] 19810710333444:
Samsung S7 Edge here, Android 7.0.

My notifications were inconsistent. Sometimes they apeared, and sometimes dont. Sometimes that was WITH the sound, and sometimes - after two sounds, the third incoming message was mute, notification only apeared in upper tab, and thats it. That was the case with two apps - gmail, and fb messenger.

I have tried all above solutions, and nothing worked for me. What DID the trick?

GMAIL:

I have hidden Google's Gmail app (it can't be uninstalled on my device), and i'm using samsung's native email app. In settings of this app I have checked the setting to synchronize automatically upon delivery:

Tap the three lines icon on the left.

Tap the cogwheel icon

In the "accounts" section tap your gmail account name to go to its settings

In "synchronisation settings" section tap "synchronisation shedule"

Choose "automatic (upon delivery).

Done. Should work.

FB MESSENGER

Here is more tricky.

Install Facebook Messenger Lite (by Facebook)

Login to yout account in the Messenger Lite

Uninstall original Messenger app (mine version was: 147.0.0.25.86)

Download the earlier version of Messenger. I have used 73.0.0.15.70 from apkmirror dot com (forum does not allow me to post direct link, sorry). Install it (remember to allow your device to install apps from unknown sources), and log in with your fb credentials.

Now you have literally TWO messengers on your system - the standard one (v73), and the lite one (newest version).

Disable automatic updates of messenger (Google Play Store will LOVE to update it, don' let him do it!)

Now, you're done and things look like this: the Lite version works as a notification provider, and the Standard version is for usage. Meaning: I don't know HOW this magic works, but those two apps should be installed on the system and when it is so - the notifications of Lite version start to work (and those from Standard version follow, but silently; this is the downside - you end up with double notifications in the notification panel). When I uninstalled either one of those two - Lite, or Standard - notifications wouldn't work.

DOWNSIDES:

can't use Gmail app

have to live with double visual notification from messengers in notification panel

have to live without the ability to view GIFs sent from Tenor GIF addon installed in the newest messenger (you get the info to upgrade messenger to the newest version. But.... you can *send* GIFs (magic as f***), and you can receive gifs from Guggy GIFs (more magic).

you ask yourself why the f*** you're still on android???

you live with constant fear that SOMETHING is gonna brake in above fragile stability at any time.

PS: My devices system language is polish, so please forgive intuitive translation of settings names.

PS2: If this gonna work in your case - then I'm starting to think that the fault lies in Facebook aps, not in the Nougat. But those are only speculations, since I'm noob with no knowledge.

PS3: feel free to contact me via email if you like to exchange info about above method (miczallegro@gmail.com). I will try to respond as quickly as possible (polish or english, please).

Regards, Micz