@Francoisf30 Hi! I completely understand the issue here. It would've been nice to be able to switch households at any time, regardless of whether or not sims have loaded into a lot. However, I agree with @luthienrising that it's working by design and perhaps creating a suggestion or feedback post would be better. This feature was intended specifically for the For Rent pack; allowing players to switch between households within the loaded lot, i.e. the rental lot with multiple households. Other than the new rental lot coming with FR, it's really only useful when played sims visit each other.
