[Too]

Killing idle apps, including Services, is a feature in Android to conserve battery life and to give memory to Activities in more recent use. This might not be as noticeable on high-end-phones.

A lot of shitty written apps are not aware of this and think they can run some while loop in the background to poll their own backend 10 times per second. Eventually that will get killed.

The solution to this is the push apis, or for apps that truly need a background loop to present a persistent notification aka "foreground-service", so the user is aware something heavy is going on in the background. Hearing FCM, which is the suggested push solution, having delivery issues above is not very comfortable.