Thanks Yuri -
Good catch that the screenshot of Mission Planner shows 4.5.5 “stable”. I installed the “beta” to resolve a GPIO problem.
reference: GPIO Relay for Camera Trigger not functioning after upgrade to 4.5.5
It appears I did this update just before 4.5.6-beta was released - so when I selected “beta” it took the 4.5.5-beta. Which coincidently, solved my GPIO problem. I simply failed to notice that it wasn’t 4.5.6-beta.
So I’ve now done the firmware update to 4.5.6-beta - and my COM port problem remains - Qgroundcontrol only recognizes the SLCAN COM port.
I have a feeling that when this problem is resolved, I’m going to learn something interesting.
Thanks for your help Yuri!