I'm in the same boat. When the pack released I prepared several rental residential lots, but I only set units for a couple of those. Meaning there are several lots in my game where those units are still part of the base residential household, that was hardly played while waiting for announcements that all bugs were fixed. I'm still not sure wat was fixed regarding he For ERent problems.
My take is that unit tags were among the problems. Simmers setting unit categories/challenges etc, then reverting lot category or making other adjustments caused trouble. And I still believe that most problems came from downloaded residential rental lots from gallery, where the simmer could nt know what the builder had done with unit categories in the past. So, I think I would double check that all unit categories/tags are cleared before making any adjustments to the rental lot.
I will need to do some testing to start actually using the rental units I did prepare nearly a year ago. Backing up my game folder as I write. My plan is to avoid landlords, so I will not let any played sim own the lot, and maybe set the rent to §0, but handle the ownership and rent manually in my spreadsheet. I wn't ever play the Landlord anyway, it seems too tedious for my massive rotation.