The "Tales from the Frontier" book had the story "Children of Zeus" involving some of the "missing".
LTT 15493 was the system named, which is ... odd. The story is set post-Alliance, so some time in the last century. The conversation makes it seem like the system is quite some way out from Sol (and possibly rimwards) - but that system is just on the edge of the bubble nowadays.
The story is probably not referring to that system, but it might be worth taking a look anyway - the book says first planet molten-temperature metal rich or HMC, and fourth planet earth-like. Anyone in the bubble at the moment to check and post a system map?
If no-one else does, I will check it when I return from Alnilam - be a few hours yet though.
(edited to add) I have arrived in LTT 15493. I could see the system map already through UC, so hopefully everyone is able to.
There is an Earth-like world (Jarek's Folly), although it's the third planet not the fourth. There's a named gas giant (Sun Dancer) close in to the star after an asteroid belt, and there are five other planets, three of which can be landed on.
The system description says something along the lines of "nothing to see here, move along." I will have a poke around.
(edited to add) No lights are visible on the night-side of Jarek's Folly. There is an odd little storm on Sun Dancer but nothing special. I've investigated a few signal sources and found nothing more than factionless pirates and wrecks. Continuing to nose...