FCM High priority Message not received in Deep Doze mode testing

Question

I start testing the app in deep doze mode by using the commands:

$ adb shell dumpsys battery unplug
$ adb shell dumpsys deviceidle force-idle
$ adb shell dumpsys deviceidle get deep

Last command to check if device is in IDLE state or not.

When High priority push send to the device, app shows the full screen intent notification to show the calling screen.

At initial the push received and screen is shown, but after 3-5 push it doesn't received. Also, when I see the logs, it shows the push is received with high priority but it downgraded to normal:

Priority: 2 
Original Priority: 1 

In onMessageReceived(remoteMessage: RemoteMessage) method using:

remoteMessage.priority
remoteMessage.originalPriority

These are the call invite high priority pushes so the ttl is 0.

Please help me to know the following:

1. Is adb command $ adb shell dumpsys deviceidle force-idle not good for testing and making test result wrong?
2. Is full screen intent are no good to prevent the bucket fill to downgrade the priority, as happening in our case?
3. Is there a way to handle it, so that app receives the high priority push every-time even in doze mode.