Inner walls won't cut away anymore

@Lailantie I'm not positive that I'm completely following, so please bear with me. I would appreciate it if you could add screenshots to a description, or perhaps share the build to the gallery so I could have a look. ( Directions in the spoiler tag for sharing to the gallery for testing, if you end up needing this: )

Personally, memory is that half walls never cut away – which can be a pain in the butt in some situations but useful in others where you want to prevent cut-aways. I did just go into my game to confirm this and I found that the half walls and half wall rooms all stayed up at all cutaway settings for me at all heights I tested. Annoyingly, though, I did find that when I used the 'half wall enclosure tool' the ceiling gets deleted:

I'm not sure if this is new or if I've always just used the 'half wall drawing tool', and when using this tool to make a 'room' enclosure the ceiling does not delete:

Since you said you did a game repair to 'get skin back', I'm assuming you may have CC/Mods? You may want to test to see if the issue is gone if you remove the Mods/CC, the cache file, then do another game repair. Directions for this are in the following spoiler tag:

I look forward to your additional information.

@SheriGR  thank you very much for your detailed reply. I deleted the buildings ☹️ It was not about half walls. It was a big room in which I built five smaller rooms, and the walls of the rooms inside didn't cut out and I didn't see my sims. I will write more tomorrow, thank you and take care

@Lailantie Thank you for your reply. I look forward to hearing about your additional findings!

@SheriGR  There are three modes to show walls. Have them all up, have them all down, or have it so only the outer walls show and the inner walls don't show. I usually play with outer walls on, inner walls off. For a few days my inner walls won't completely disappear when I go into that mode. Like, I have a room and build a little bathroom with two additional walls. I can't see into the bathroom, I see the bathroom walls instead. And I don't see my sims in the bathroom because it is too small and I can't cam in. It seems as if this mode of having inner walls set to not be shown is broken.

I was so frustrated with that whole thing that I started a new game with only one sim and a dog and two little huts on the beach where there's no walls blocking my sight. I will do more testing with older and other buildings to see if the walls cut away there or not.

I mentioned the game repair as I had two corrupted files in my game which made a skin not show on a young grownup sim, whereas it was fine on the teenager and the grownup. And I don't use any CC for skins, just for a few hairstyles.

@SheriGR  So I tested with my new savegame and the walls behave just fine.

So my question changes into another one: why is it that whenever I play a savegame for a long time, like the last one (I was in generation 9 and somewhere in the middle I set the time to long), the game breaks and I get the weirdest errors?

Like the skin for young grownup missing (default skin), or one of my mermaid teenagers not having a fin when swimming while all the others have a fin, or that thing with the inner walls not hiding anymore.

The plants behaved strangely and I never knew if they would survive if I removed the weed. Walking the dog was almost impossible because of the lag, my sims would stand there for ages until they moved. Fast forward during the night had one of my sims almost die of red bars as he couldn't move or care for himself.The dog would only lay down on his pillow if I stopped fast forward.

And then the toddler issue, it is already a pain in a young savegame when four grownups have that toddler image in their to do list and the toddler is almost starving as each of them wants to feed him. And whenever someone finally manages to put him in the chair with food, the next one takes him out, puts him down, back up and back down, then walks away until the third one comes, puts him into another chair and then finally puts food on that second chair. Unless he is blocked by the fourth grownup who also wants to feed the toddler or maybe better bring him to bed, hungry as he is, because he also lacks sleep.

I would have put up with all these issues, but the wall thing really ruined the game for me. Is there any way to make longer games work better?

@Lailantie 
High Chair:
Honestly, I never use the high chair for gameplay. @PugLove888 and I have a nick-name for it: "The Evil Highchair"... for exactly the reasons you mentioned. If you have several adults &/or teens in the home also, as they will all respond like that to a toddler vs. high chair, especially if the toddler is in distress. Insanity. I have screamed in frustration and fear for my toddler before in this circumstance.

What I do instead is drag a serving of food/plate of food/fruit or veggie for them onto a surface they can reach (leftovers are your friend). I direct the toddler to grab it, and they sit on the floor or a nearby chair autonomously and eat it and everyone is happy. If you have the 'Movie Hangout Stuff Pack' you get a popcorn maker. If you have an adult make popcorn it never goes bad in the machine, so the toddler can be directed to grab a bowl from it. Apples for snacking apparently also give a mood boost (trying to remember - happy?), and you can put other fruit/veggies out (they don't spoil), also have the toddler keep some in their 'personal inventory' for when you're in a pinch. I don't think they'll grab these on their own, but you can direct them to eat them.

Walls:

The three settings for walls are up, down, and cutaway, to my understanding. Cutaway (my normal choice) varies considerably if you have small rooms and some other types of wall setups and room shapes. I find very tiny bathrooms annoying to deal with, true. You can view then by temporarily dropping all walls. I also run into some funky business on cutaway mode in some of my tiny homes for the same reasons - when I have tiny rooms or nooks, very small loft rooms, etc. In those cases to watch in live mode I need to also drop all walls when they are in a room like this. 

Lagging:

I also tend to have  a lot in my game saves, and probably have more game saves and library items than I should, as I do have times my game lags a bit. I periodically things like clear out some of the game saves, library items, adjusted graphics settings, cleared cache files, close browser windows on my computer and open programs, and adjusted households limits to help. I also don't use Mods/CC. I own all packs.