----HOW TO GET PUSH NOTIFICATION WORKING----
In order to get push notification working (well) you have to follow ALL THE 6 STEPS of this guide :
1/ LOCK DESIRED APPS IN RECENT APPS LIST
Launch all the apps you want to get notification from > Open “Recent” and lock desired apps by long press on them, a padlock will appear
2/ ENABLE AUTO START FOR DESIRED APPS + GOOGLE SERVICES APPS
Go to Security app > Permissions > Auto-launched apps : Activate desired apps + Google services apps.
3/ ENABLE BACKGROUND RUNNING FOR DESIRED APPS + GOOGLE SERVICES APPS
Go to Security app > Power > App managemnt : Activate your desired apps + Google services apps.
4/ PROTECT APPS FROM THE ACCELERATOR
Go to Security app > Accelerator > Settings > Memory acceleration whitelist > Add to white list : select desired apps + Google services apps then click OK.
5/ CHECK THAT SYNC IS WELL ACTIVATED
Go to Settings app > Other Account > Your Google Account : SYNC ON + Gmail/Inbox… SYNC ON
6/ REBOOT YOUR PHONE AND CHECK IF IT WORKS