In Android, the Application#onTerminate() method doesn’t seem to work on actual devices.

public void onTerminate ()

This method is for use in emulated process environments. It will never be called on a production Android device, where processes are removed by simply killing them; no user code (including this callback) is executed when doing so.

[Source]: Application#onTerminate() | Android Developers

For more details, refer to the following articles.

・baroqueworksdevの日記: Application#onTerminate()がコールされない

・La chiave a sviluppo del software.: Application#onTerminateは、実機では呼ばれない。

That’s all from the Gemba.