I've continued to experiment and this is where I am now. I have a spare Nano Connect (with problems reading and writing to pins) that I'm experimenting with. When I connect it to the USB, I am able to see it on the device manager and via the "Select Other Boards and Port" tool, and I can upload and run a simple sketch (output to the serial monitor). When I detach the new Nano Connect from its Screw terminal adaptor and connect it to the USB, it now shows on the device manager and via the "Select Other Boards and Port" tool, and I can upload and run the same sketch and watch it run on the serial monitor. When I plug the new Nano Connect back into the Screw terminal adaptor, I no longer see it on the device manager nor via the "Select Other Boards and Port" tool, nor can I upload a sketch. I'm going to disconnect all wires from the screw terminal adapter and see if that solves the problem, then slowly add everything back one at a time to see if that identifies the issue. Wish me luck.