Undefined Component

I've got an intermittent connectivity issue (choppy audio, some zone players refusing to become part of a group. one zone player sometimes neglecting to play when its Alarm is triggered). It doesn't happen all the time, but I would like to get back to the rock solid reliability that I had.

I have recently added equipment (Playbar, Sub, Samsung TV, probably other items I have forgotten), so things are more complicated than they used to be.

All of my Sonos components now have reserved IP addresses in my router (though currently only one has claimed an address). The entire network and all devices that connect to it have been powered down and back up.

When I review the support matrix (. . . :1400/support/review) I see 9 rows (one for each Sonos component) and 10 columns --> there is an extra column for "Strength to 00:0E:58:B0:92:10 undefined".

That MAC address does not appear in my router's leased DHCP list, and is not an authorized wireless client of my wifi bridge (my wireless access point is locked down pretty tight).

What is this mystery component?

Is there somewhere I can read about the matrix and other diagnostic info so I can better understand my system?

Thanks in advance for suggestions, or pointers to reading material.