Sind beide Apps mit dem gleichen Zertifikat signiert? ("By signing multiple APKs with the same certificate and using signature-based permissions checks, your apps can share code and data in a secure manner.",
https://developer.android.com/studio...considerations)
Ist ein Shared User in den Manifesten eingetragen? (In order to share data between apps (provided they are issued by the same publisher) you will need to specify a shared user id in the AndroidManifest.xml of both apps. -
https://stackoverflow.com/a/7935032/80901)