If I had to guess, I would be willing to bet that the OP saw an RNG crashed satellite thingiemahjigger. The first time I saw one of those on an abandoned planet, I thought I was fittin'a be forum famous. Then I found out what it was and felt a bit silly. That's what I'm guessing happened here.
One of the nice things I find about these mysteries is the way that lots of people will go "I went to system which may or may not be associated with the mystery and found a POI / signal source / NPC / rock - could this be a clue?"
And sure, it's never something actually relevant to the mystery, or unique to that system, or even particularly unusual. But it's getting people out and about seeing the great variety of interesting things that
are definitely in the game but which they might ordinarily pass by without looking at while running trade goods or grinding materials or whatever.
As regards what Raxxla
is my best guess is that:
1) It is in fact some sort of mystery portal, but to stop Frontier having to implement an entire destination for it before they're ready (or perhaps even in this Elite) it's turned off, there's no obvious on switch, and there isn't a cargo pod labelled Raxxla Owner's Manual floating nearby.
2) It's a POI, so stored server-side where it can't be data-mined or detected from outside the system.
3) It's made up of existing assets, but put together differently, so that its existence can't be inferred from data-mining. It was probably a Coriolis toastrack with some bits stuck on in 1.0, because that's all they had that looked vaguely gateway-like (and would explain the existence of the toastrack). Nowadays it might look a bit nicer.
It would be hilarious if Raxxla was Shinrarta Dezhra or had something very closely tied to it in the system, when people are searching all over the galaxy lol
My "it was there all along" guess is that Raxxla is the moon "Ra 10 a"
RAXXLA = Ra + X + (XL) + a
X = 10 (Roman numeral)
XL = extra large (size)
So it's pointing to Ra 10 (which is the largest gas giant in the Ra system, and pretty big as gas giants go in general, hence 'extra large'), moon 'a'.
This fits the Codex comment that some theories say it's an unremarkable moon, which Ra 10 a is. Irrefutable Proof!
(To cover all possibilities, the Codex and its statement about unremarkable moons was added several months
after I first published the "it's Ra 10 a, no-one said Raxxla had to be interesting" theory, and "Frontier are trolling me personally with that line" is about as plausible as the chain of events needed for the Kwatis theory to be right, so...)