android 6.0.1 adb,adb - Android 6.0.1 uiautomator SyncException: Remote object doesn't exist! during...

Objective: I want to automate call related scenario using android uiautomator in android 6.0.1 devices. But not able to get UI hierarchy in incall screen (Mute, Spearker On, Keypad, Addcall etc.)

Note: I am not using any appium server

Error: "Error obtaining UI hierarchy" Reason: Error while obtaining UI

hierarchy XML file: com.android.ddmlib.SyncException: Remote object

doesn't exist!

Observations:

adb devices is listing the device and we can access /data/local/tmp/ directory

restarted device, restarted pc, relaunch of uiautomatorviewer

adb shell input tap x y is working (but don't want to use co-ordinates in scripts files)

please assist in finding a solution in order to automate phone app incall scenarios like "mute" , "unmute" , "dtmf pressing keypad numbers", "speaker on" speaker off".

Is there any way to perform such actions via adb ?