FCM notifications token NotRegistered error

Hi,

I have a very strange problem regarding notifications-v2 on some Android devices.

My application is basically a multiplayer client-server game.

When a player opens the app, I call notifications.getDeviceToken(), get a valid token and then send it to my application server to be stored on a database for later use. 

The weird thing is: for %10 of my userbase, I am getting “NotRegistered” error message from Google FCM servers when I try to sent a notification to users. I also used firebase console to test the validity of the token and firebase console also states that the token is invalid.

How is it possible that getDeviceToken() function returns an invalid token? I really dont get this.

Do you any fellow corona developers experienced this issue before, or am i missing something very obvious here ?

Thanks for your time.

deniz.