We met the cultists at The Moist Hatch and they seem to know a lot about slipstone but had strange gaps in their knowledge. And the things they knew seem to be from anecdotal / folk knowledge rather than scientific knowledge. They wore pendants of slipstone around their necks.
A couple cultist ships ambushed us at the slipstone dead drop. There were also a couple cultist ships in the remote system we explored. In both cases the cultist ships were accompanied by Svarogian ships. The cultists wanted our cargo of slipstone and were willing to risk death (when Dr. Argonine threatened to destroy the entire system using slipstone magi…science).