This is weirding me out.

Subscriber called to complain home devices weren't performing properly. Remotely examined his hAP lite WiFi AP. Saw two devices registered, each showing signal varying wildly and quickly in the range from -60 to -90. I suspected wireless interference, so I ran a background scan. Found an un-named SSID with a private MAC address occupying the same channel with strong signal (see highlit line in image).
The subscriber and I spent a little time attempting to determine what other AP existed in his house, without success. Finally, just to get the problem fixed, I moved the hAP lite to another frequency. When I rescanned, I discovered that the mystery AP had also moved to the new channel! Another couple of changes confirmed that the mystery AP had to be the radio card in the hAP lite itself.

Now, this bogus AP shows up whether the scan is a background scan or not. If the scan is not a background scan, the radio card's AP function should be entirely disabled, and yet there it is. It also has no radio name, which I would expect from a MikroTik AP that has a radio name.

I remotely examined two other hAP lite units at two subscribers installed the same week. Neither showed this behavior. (No surprise, since I have never before seen this behavior.)

I did an export verbose of the wireless section and examined the output by hand to see if perhaps I had inadvertently enabled some parameter that would activate the "repeater mode" feature of the newer ROS software. I couldn't find anything related. Obviously, I first ruled out the existence of an additional virtual AP.

I upgraded to the current ROS and rebooted. No change. I reset the configuration to no-default and rebooted, executing the customer configuration script after boot, to entirely reinitialize the router. (I couldn't netinstall because it was remote.) No change.

Before I RMA this box, can anyone propose an alternative explanation for this behavior other than bad hardware?

Chromecast devices create a strange "AP" like that.

It's the guest network

Thanks for the pointer to hwaddress.com. My two go-to websites for decoding MAC addresses showed fc:a6:67:0e:81:96 as "not found," so I assumed that it was a private address made up out of whole cloth. Looks like it's time to switch reference sites.

I've never played with a Chromecast, but from the online instructions it seems to offer a temporary configuration AP, like a Ring Doorbell (which I have setup). Like the Ring, that AP is supposed to disappear once the device is configured to the home AP. But unlike the Ring (which has a reset button) if the Chromecast loses the home AP, it immediately presents its own AP again. And apparently it always chooses the frequency on which it last saw the home AP. Meaning that if the Chromecast has a spotty connection to the home AP, it will proceed to compete with it on the same channel, a design with unintended consequences.

That explains all the bad behavior I have been seeing. Thanks, all.