For some reason, Somerville Place and the Slog belong to the same leader and if you change it in one, it will change in the other. I even tried to scrap both settlements, remove city plans and leaders, but it doesn't fix my issue: I'm still getting the same leader for both settlements and, apparently, even the same max stats (for example, if I build the Slog first, they need 20 inhabitants in the city and it will get the same amount on Somerville; viceversa, if built Somerville first it will get 17 maximum inhabitants for both cities. Anyone has the same problem?