raix-push: Android Client no longer registering after upgrade

After upgrading from Push 2.6.12 to 3.0.0 my Push notifications stopped working on Android.

When I run my app in a browser, the logging (with Push.debug=true) shows:

Push: Settings userId "qwertyuiopasdfghj" for app: mnbvcxzlkjhgfdsap

When I run my app on Android no such message is shown.

In both cases (logged in on Android or in Browser) when I Push.send I get:

Push: Send message "blablabla" via query { userId: 'qwertyuiopasdfghj' }
Push: Sent message "blablabla" to 0 ios apps 0 android apps
Push, GUIDE: The "Push.appCollection" is empty - No clients have registred on the server yet...

This is intended when logged in on the browser, but not when logged in via the Android app.

The upgrade to Push 3.0.0 included an upgrade from Meteor 1.1 to 1.2 and the inclusion of Crosswalk. Removing Crosswalk didn’t help.

What keeps my Android client from registering?