furniture disappears when unit is rented

just got For Rent. I created a 6 unit building, fully furnished, rented out a couple to 'unknown' Sims, then created a new family to rent out another unit.  All the furniture is gone when I move them in.  There was no option to rent 'furnished' - it told me that wasn't available (when I rented the unit as the new family).  Why did I waste my time wedging all that furniture into that small space if it just goes away?? How can I get it to stay?

playing on a mac OS 15.5 -thanks in advance