I think a couple of the slrpnk mods have wormed their way into the good graces of the admins there and then used the anarchism as cover for pushing authoritarian agendas.

That's exactly what I think. I don't think that it's slrpnk as a whole but that anarchism comm on the instance had very problematic mods (who have indeed gone silent, pretty much proving that they were bad faith actors). They constantly acted to spread propaganda and silence anyone who disagreed. IIRC, one even all but outted themselves as a state actor. They're all quiet now because they got what they wanted; successfully sewing enough discord in anarchist and other anti-authoritarian communities to prevent critical mass or embrace of effective strategies for positive societal change.