Some Chinese Android manufacturers make use of custom power-saving restrictions that inhibit sending push notifications to your users while your app is in the background, swiped away from recent apps, or after a device restart.
Most notably, Chinese market devices from the following manufacturers include custom power-saving restrictions:
In order to receive notifications in the background on these devices, there are two options:
1) If the affected devices are not within mainland China, we recommend implementing FCM high priority fallback delivery. This is proven to work around several of these manufacturers' custom power saving mechanisms (Xiaomi, OnePlus, and more), by having Pushy deliver your notifications through MQTT and Firebase Cloud Messaging's high-priority channel simultaneously, while only waking up your app once.
2) Display a dialog asking your users to whitelist your app from the respective manufacturer's power saving mechanism, within the device settings. The steps for achieving this are different for each manufacturer.
More info about this issue: