Denys,

Please note that Kinvey has not yet migrated to using FCM and therefore the Android SDK and server setup are still using GCM for sending and handling push notifications. Therefore, using FCM in your project would cause the Android SDK to not perform as expected when registering devices and handling push notifications. Today we support the Google Cloud Messaging (GCM) service. It is our recommendation that you integrate your app's push notifications using GCM rather than FCM.

Anyway, please try following things and see if it helps:

1. Please make sure the 'Sender Id' and 'Server Key' in the Kinvey Console are the same as your Firebase project.
2. Have you tried sending push notifications to multiple devices or just one? If not, please try sending it to different devices and check if they receive it.
3. Make sure you have followed each step mentioned on this link.
4. Please send me the userId (_id) and email address of the user (for which "_messaging" field is getting populated) you are trying to send the push notification to so that we can investigate in our server logs to try and see what happened.
5. You can try sending push notifications from BL using this link and see if it works.
6. From our logs, I see that you are using Android 3.0.16. Please try updating the Android SDK to the latest one and see if it makes any difference. Here is the link - https://devcenter.kinvey.com/android/downloads#

Thanks,

Pranav