---- EDITED 26. August for summarizing the history of original issue and needed solution

Google has updated the push messaging infrastructure to FCM and will retire the old setup called GCM in 2019 (https://firebase.googleblog.com/2018/04/time-to-upgrade-from-gcm-to-fcm.html).

Hence apps are moving over to use FCM and stop working with current GCM features of microg. This results in different app behaviors. Some apps do not receive any push messages anymore, others (like Whatsapp) fall back to a polling mechanism, that uses lots of battery.

To use updated apps again with microg, the GCM functionalities mimicking google service framework will need to be updated to FCM.

---- Original Issue that lead to missing FCM functionality issue
Hi there,

I have a strange behaviour on my phone with GCM on AOSP Oreo. Some apps can register for GCM, even push notification tester works flawless. However Whatsapp and Threema won't register for the service.
I regularly get the message "GmsGcmRegisterSvc(6107): registration not allowed".

So far I have the feeling, that the "ask for new apps" function is not working properly. As it was enabled in the beginning (When installing Threema and Whatsapp the first time), but not anymore.

Is there a way to clear the list of registered apps and start over? This is just a hunch now and want to test this, before digging into other things.

Regards
Chris

P.S.: If you have any other idea, let me know. Can also produce some logfiles.