Sims can't walk through open area
Ok. I downloaded the lot. I see where you have the access problems on the second level. Back room in apartment 2 and the center section of apartment 3. I don't have any good news for you. I tried everything I know to make those areas accessible. It's not route blocks. It's something about those rooms that is stuck so the game just won't see the inaccessible spaces as rooms. That might be due to mods and CC but I don't think so. I think it's something else.
I was looking at your download and noticed that it was a lot you downloaded created by somebody else. So, I hunted down the originals (there are 2) in the Gallery, downloaded and tested them. They have the same problem in the same places. So, there is nothing you did that caused the problem. The problem is with the downloads. Both of the lots were a residential venue in the Gallery download but one was furnished and the other not. Judging by the pics on the download of the furnished version, I can see apartment 1 is fully furnished but apartments 2 and 3 aren't and show the same as they would if the apartment venue was residential rental when a sim is on a lot where the only apartment you can see is the active one and the others are hidden.
What I think has happened is the original creator had the lot set as a residential rental and then changed it to a regular residential right before uploading it without removing the space assignments first and probably with a sim on the lot who owns it. There are a lot of those on the Gallery that way that people uploaded with the lot owned and/or a sim on the lot. You can't do that with residential rentals. They may work fine for the creator but don't for others who download the lot. The only one who can fix the problems with those lots is the creator, if they can be fixed at all when that happens. Usually, the Gallery upload has to be replaced so the lot works for others who download it.So, I think you'd probably be better off scraping this lot and either find another on the gallery that doesn't have issues like this one or building your own.
Hope this helps.
