Tell user that he needs to change battery optimization on his device to get background notifications

[Nostradamos]

The problem is that many vendors ship roms with a battery optimizer which disables background activity on apps which are not in a whitelist (like whatsapp, telegram etc.). So if your app is not in that whitelist, the app can't run any background tasks like checking for new messages etc.
Threema somehow managed to figure out if the smartphone rom has such an battery optimizer and informs the user that they have to disable that feature or have to whitelist the app. I guess this would be quite helpful for Riot-Android.
Besides that we should also put this in the FAQ (if there's any), that if you don't recieve notifications, you maybe have to check if your android is doing some battery optimization tricks like this.