Just wanted to check in and cross reference some findings with you all.
Those of us out exploring in the 'Formidine Rift', although not necessarily a relevant mystery, have also located USS's in Systems near to and inside the Heart Nebula. Interestingly, as far as I can report, there are no occurences of such USS's spawning in the Soul Nebula.
Could it be possible that UA's and Barnacles might also exist in the Heart Nebula?
this has led me to believe that these USS's which contain a wrecked ship and Data Caches are somehow connected to the Formidine Rift mystery... however reading the previous post in this thread mentioning the same USS's spawning in and around Barnards Loop Nebula
and inside the California Nebula, and Drew Wagar's cryptic comment about "Nebulae are good places to hide things" and I think there may be some connection between these two mysteries, or at the very least an interesting find regarding the likelihood of USS's spawning outside the bubble but specifically inside Nebulae.
For those of you UA/Barnacle researchers not familiar with the Formidine Rift (as I assume the two mysteries have diverged somewhat) you can find the thread here.
https://forums.frontier.co.uk/showthread.php?t=252932