QGCS not seeing Pixhawk 2.1 on connection

Strange one this. We are experienced users of Pixhawk (have built and supplied to customers hundreds of aircraft with Pixhawk) although have not used PX4 code for some time (tend to use Arducopter). We have found that QGCS is not seeing a Pixhawk 2.1 cube at all when connecting and so cannot upload the flight stack. We have two versions of QGCS V3.4.4 and the latest V3.5.6 and so far have tried with both versions on three different laptops and with three different brand new Pixhawks. On connecting the USB, the laptops acknowledges the connection to the device but QGCS does nothing and remains ‘Waiting for vehicle connection’.
I am not seeing anyone else here mentioning this, so I am wondering if anyone has any thoughts or comments?

They’re shipping without firmware so it isn’t immediately obvious that they’re detected. Have you tried uploading? Or using Missionplanner to put an initial firmware on, then using qgc?

auturgy Thanks for the reply, the answer is yes, we have Arducopter 4 installed with no issues, but QGCS still does not see the autopilot when connected. The last time we used PX4 was about 18 months ago, and we had none of these problems then, all seems a bit strange, and as others are not reporting this I suspect it is something we are / are not doing, but have no idea what that might be at this time. A bit frustrating!

Perhaps try a daily build of QGC

same issue here. you have to use the daily build of QGroundControl. this has fixed it. i have also get the PX4 stack flashed with mission planner. but i think it was luck and i cannot reverse the procedure with another cube.