so-called SmartNID were futile. Reddit to the rescue as I am far from the first to experience these problems.

According to the Quantum Fiber "book" for my model router/gateway, a factory reset to defaults is done be pressing and holding the reset button for about 10 seconds. 15 seconds or longer supposedly results in a mere reboot with current settings. As it turns out, that is rubbish. It takes holding in the reset button for about 30 seconds to get the thing to reset to defaults. Anything less than 20-30 seconds is just going to result in a reboot.

When I was finally able to get the thing to re reset to defaults, I was then able to reconfigure it as a transparent bridge by starting over again. It actually did take about 30 minutes for it to phone home again and establish a connection to the Internet.

All is well now but I was up most of the night getting things to work properly and doing a lot of waiting.