Slaves either join me immediately or just have their AI broken and stand there until they starve without following me. Idk if it has anything to do with the 256 follower mod, but before I downloaded this I would just save scum with buying each slave individually. Now I still have to do that so they don't just break the second I purchase them.

I was having this difficulty when I was testing the Experimental branch version of this mod, one of the reasons I chose to rewrite it in Stable was because this kept happening. There hasn't been any game updates that I know of since this was made, so I'm wondering if it has anything to do with one of your other mods. This isn't likely to play nice with other AI mods regarding slaves, but I don't know which ones will work with it and which ones won't.

Essentially all I did here was go into the FCS and delete "doesn't join player faction" percentages and boosted the chance they do join to 100%, or added "joins player faction | 100%" to the ones missing it, and rewrote the text in their dialogue to go along with this. It sounds like a mod conflict, or maybe Stable doesn't play nice with Experimental in the same way Experimental didn't play nice with Stable.

If you haven't tried already, load this mod at the bottom of your load order and see if that fixes it.