Mobile Push Notifications: send to unknown device

Rocket.Chat Version: 0.55.1
Running Instances: 1
DB Replicaset OpLog: Enabled
Node Version: 4.8.1 - x64

Users ~20
Push Notifications: by Gateway https://gateway.rocket.chat

Hello,
I have problems with my mobile push notifications. I recieve them only sporadically. Also my users reported problem to me, not recieving notifications with newly installed apps.

I tested different devices and also saw some inconsitencies of the mobile push notifications. Only desktop notifications had no problems. Later I uninstalled all apps to have a clean status. But one device remained and I dont know how to remove it. Here you have some logs.

Configuration

Push: configuring... 
Push.Configure { sendTimeout: 60000,   apn: undefined,   gcm: undefined,   production: true,   sendInterval: 1000,   sendBatchSize: 10 } 
Push: Send worker started, using interval: 1000 
...
Push: Settings userId "y6q3zXXXXXXXXX" for app: FjfXXXXXXXX 
Push: Got push token from app: { id: 'FjfXXXXXXXX ',   token: { gcm: 'c_3XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX' },   appName: 'main',   userId: 'y6q3zXXXXXXXXX',   metadata: {} } 
Push: updated { _id: 'FjfXXXXXXXX ',   token: { gcm: 'c_3XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX' },   appName: 'main',   userId: 'y6q3zXXXXXXXXX',   enabled: true,   createdAt: ...,   updatedAt: ... } 

I did some test pushes. The app was uninstalled and the token was deleted. But one token remained.

Push: send message "@sscholl" via query { userId: 'y6q3zXXXXXXXXX' } 
Push: send to token { gcm: 'dudcB_MOnXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX' } 
Push: send to token { gcm: 'c_3QXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX' } 
...
removing push token c_3QXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 
...
send to token { gcm: 'dudcB_MOnXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX' }

Are Chrome Notifications also appear in this context? That could be, that this is the chrome notification.

Do you see general problem with my configuration?

Thanks.