I get Error [px4flow] PASS when I run px4flow test in mavlink console! (PX4Flow+EKF2)

[rhamrah]

Hi,
I am using an optical flow sensor which has a sonar, plus EKF estimator, not using GPS. The flow sensor is connected to a Pixhawk through I2C port. The QGC version I am using is 3.4.4 the latest one, and the PX4 firmware is 1.8.0dev for a zmr250 racer airframe. I've also set all required parameters in qgrouncontrol as:

EKF_AID_MASK = 2,
EKF_HGT_MODE = Range sensor,
SENS_FLOW_ROT = YAW 270 deg,
...

and I am receiving and seeing all optical flow data on Mavlink Inspector in QGC, but I do not know the reason of ERROR [px4flow] PASS I get in Mavlink console of QGC, and what it means! In Mavlink console, when I start px4flow it says:
WARN [px4flow] already started
When I stop it and start it again, it says:

INFO [px4flow] scanning I2C buses for device..
PX4FLOW on I2C bus 1 at 0x42 (bus: 100 KHz, max: 400 KHz)
PX4FLOW not primary range device, not advertising

What it shows when I run px4flow info is:

When I run px4flow test, it shows:

and ends up with ERROR [px4flow] PASS .
Can you please let me know what this error is, and why px4flow is not considered as the primary range device?!
I've also flown the drone, and when I switch to Altitude mode the drone flies up vertically and it seems px4flow sensor doesn’t work properly. Please let me know if you have experienced similar issue, and how to fix it?