Got off my butt to finish the last bit of the story. So it's leaning more and more towards the CSC became the Fractsidus and Rover was the creator of both, right? The Fractsidus know about the inner workings of the Sentinels, Threnodians, Sentinel permissions, the Central Hubs controlling things like the Beacons which the Sentinel itself created, Tacet Discords, Echoes, frequencies in general, and how Rover is tied to all of it. Things even the Black Shores don't. The common knowledge is that the CSC just outright disappeared one day, and the major facility of theirs we explore was experimenting with TD frequencies and trying to get them under control. Everything we learn about them is that they were also massively technologically advanced to a crazy degree compared to the rest of Solaris. The Fractidus are also carrying out experiments with Threnodians.

Since Rover has Abby who is an Echo that can consume even Threnodian frequencies, I imagine that before Rover decided on having amnesia they were directly looking specifically into dealing with the TD problem the way the current Fractsidus are doing it but the death toll was too high and Abby was a last ditch effort that has proven to have worked out so far. The amnesia is a way to give Rover an unbiased view into the Sentinels, Threnodians, TDs, Echoes, Fractsidus' methods, and reality as a whole compared to their headspace of being some godlike being in charge of Solaris.

It would also explain every region seemingly being an experiment for some aspect of dealing with reality. Jinzhou was for creating ways to fight off the Tacet Discords militarily and keep humanity alive through technology. Huanglong was dealing with the Sentinel's control of time and how it affected it. The Black Shores was using AI to run through infinite simulations of how to prevent TDs. Rinascita as a whole was about using Echo frequencies to advance humanity and protect them, possibly even endear them to the concept