infinitieunique After you install the Sandboxed Google Play Services every application begins to see it and use its notification service by default, meaning that most likely your every notification is being sent to Google
Is that the case? So far I thought that only if you install Sandboxed Play before installing the app, it will be recognized. For example I think Signal checks upon first setup and if Google Services are not present, it will keep using it's own implementation, even if Google Services are suddenly there. But maybe that depends on the app developer and differs from case to case... Or maybe I'm just wrong here... Let's hear the experts.
If you want to separate Google Services from specific apps, I'd generally recommend creating different user profiles for now...