That's.. weird. Why would Pyroclast put itself in the way of Vulcanus, and yet require Vulcanus science to unlock? I think I can see why Loup almost immediately banned the planet from his pack
I would file this under "not a bug", and recommend uninstalling Pyroclast. Basically the only fix for this is moving Pyroclast entirely, or simply starting on Pyroclast (which is likely the original intent behind the planet).
EDIT: As much as I hate moving planets, except as a last resort, I implemented the fix in v1.0.35; thank Samario for the suggested new location (behind Vulcanus, from the perspective of Nauvis).
After seeing its original location, without Cosmic Social Distancing enabled, I can honestly say that the Pyroclast dev chose literally the worst possible location for their planet. It's practically touching Nauvis, guaranteeing that it will block any and all connections when RSC is enabled.