IMHO the Ruins and the Aliens Ships/Shipwrecks/UA/UP are two separate stories, and in fact both scientists are very careful to not mention the Ruins when talking about the Sightings.
This does not mean that both stories could not be related somehow: for example these aliens (please, we know it, they are some kind of thargoids

) could be responsible of the Guardians' demise, or these two "civilizations" could have come in contact somewhere in time. But the Guardians could be about THE PAST, the ships we're encountering could be THE FUTURE.
Another thought about the RUINS:
reading carefully through the collected data, what is clear is that they are what we could call a
huge library, or Wikipedia: a way for them to SHARE ALL THEIR KNOWLEDGE each other, in a way that is described similar to telepathy: wireless

Huge Hubs of knowledge, like HOTSPOTS carefully placed, to extend THE RANGE of these "libraries", to let their knowledge be accessible further.
Imagine for a moment, each single being of this specie, being able to access the whole knowledge: each one could be everything at once: the better scientist, the better politician, the better warrior, the better everything. I'm still wondering how too much knowledge could cause the end of e specie...