He is one of the bugged Thralls.
It is documented here on how to fix it
I also created 3 mods before that posting that fixed his spawn, among others, like this mod here. So I know that forum posting is indeed correct on how to fix it.
Finally, I documented my findings to the devs in the mod discord and have provided my .csv to be publicly available on my mod pages. Anyhoo, just thought I would drop that bit of info off.