I have a new Vodafone Smart Prime 7 with Android Marshmallow preinstalled. Notifications are rather unreliable. Please note, all the usual settings are correct and I have already un-opimised the affected apps from the battery optimisation thing. With some apps, the notification seems to come through at the right time, but I get no actual alert until I activate the phone. With Whatsapp for example, I won't get any indication of a message until I switch the phone out of sleep mode. Facebook Messanger is the worst. Whenever I get an incoming message, the phone completely crashes. It removes my wallpaper and the screen keeps fluctuating between off and on; I have to physically restart the phone to get it working again (and even then, I get no actual notification that I've got a new message). How can I sort this out please? Thanks.