PX4FLOW with Pixhawk 2.1; missing Log Data!; Connection Instable?

Hey there,
I am trying to get my Pixhawk 2.1 (APM:Copter V3.5.3 Quad) with PX4Flow Sensor running. So I follwed the Manual here (http://ardupilot.org/copter/docs/common-px4flow-overview.html). So I get this all done till the Range Sensor Check. But I can´t find EKF5.meaRng message in my Flashlog, where can I find it. I just found “EKF/Height Above Ground” which seems to be right.

One other thing is that the connection between my PH and the Sensor is not always continuously. But I am not shure if it is usual behaviour. In the Status window the Parameters opt_m_x and …_y is allways jumping between “0” and something else. I just found out that untill I pick my copter up and move it around, then there is something but “0”. So that could be good and be some usual behaviour. The copter is only connected via USB.

But while I tried to calibrate the sensor I often got no sensor datas in my log files. They were just missing. So I did it over and over untill they appeared. Is there any explanation or and solution?

Thank you!
Best Regards