Can not get Headers for sinch incoming call when application is in close state for the first time only

Question

I have following code in my SinchService.

@Override
public void onIncomingCall(CallClient callClient, Call call) {
        Log.d("Size", "Size : " + call.getHeaders().size());
        Log.d(TAG, "onIncomingCall: " + call.getCallId());
        Intent intent = new Intent(SinchService.this, IncomingCallScreenActivity.class);
        intent.putExtra(CALL_ID, call.getCallId());
        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        SinchService.this.startActivity(intent);
    }

In the first line i am printing Header size. I am getting correct value for header size when app is active but when app is inactive(terminated) it is 0 for the first incoming call only.

I found the same issue for latest sinch-push tutorial also.