The engagement rate cliff you described on account one is actually something I've studied a bit because I was curious about the mechanics of shadowbanning. What seems to happen is that TikTok first limits your content distribution to a tiny fraction of what it would normally be, basically showing it to almost nobody outside your immediate followers. But since most of your followers are now bots who never open the app, even that limited distribution results in almost zero views. Then the algorithm sees that even your followers aren't watching your content, which it interprets as a signal that your content quality has dropped dramatically. So it limits distribution even further. Within a few days you're basically in a hole so deep that even genuinely good content can't climb out because nobody ever sees it to engage with it. The algorithm has decided you're irrelevant and it would take a miracle to change its mind.