Having a problem with diagonal walls after the update.

@Iamflare I am able to reproduce part of this but not all in my game. 

• I find that I can place wall decorations of several varieties plus shelves of several varieties on the walls of this diagonal room. Note: I did adjust the placement of the shelves via holding down alt and dragging them within the areas this method will allow:
  
  And in this case if you drop the walls, all items disappear:
  
  
  
  
• However, if I activate the MOO cheat and re-place three of the walls to locations that I was not allowed to freely place or place just using alt-drag without MOO...
  
  In this case if you drop the walls, all items disappear except the three shelves that I used MOO to place where the game did not allow:
  

So, this explains the items hanging in the air, but not why you are not able to place items on your wall at all without activating MOO. Can I please clarify a few things?

• Are you unable to place anything anywhere on the walls without MOO on, or can you just not place in the location you want to? Diagonal walls can be fidgety to deal with, and behave differently in several ways. Item placement can be tricky on them.
• Does this happen if you have MOO and all cheats off and draw a different room?
• Does this happen with cheats off and trying it in a different lot?
• Have you tried a game repair? [ Open Origin, click 'Game Library' then right-click Sims 4 > Repair Game ]
• If none of this seems to help, can you please upload the room to the gallery and add the exact name here along with your gallery name if it's different than your name here, so I can test in my game?

@Iamflare I was just chatting with @CGrant56 and he's got some screenshots from his game that got me wondering about something. I experimented a bit with window and door placement in my game after the patch, and I found some odd behavior that you could see in the video I ran while experimenting. Can you try removing the windows on that wall you're having issues with and try placing things without MOO on. You will only be able to place certain distances apart and some areas don't seem to allow for it. I'm just wondering if the new window placement changes have caused changes in how this is working for you? https://youtu.be/qAFrfsVYYKE

Could you share a screenshot here please?

Edit: Also, per what @CGrant56 was saying in his post, I just did an experiment on the other two walls of the diagonal room above. I found that although the game allows me to put a window in the middle wall panel, it will not let me put a shelf there. The only space left then for my shelf is to the right and left of the window... but it won't let me put it there either. However, it will allow me to put it in the middle of the right or left wall panel... even though there is a window in that spot.

I realize there's not a full wall panel left on the right or left, so that's probably the issue with this shelf, and if I extended the wall and tried the shelf over a bit I expect it would work. Is it possible that your wall is short like this one and that may be your issue?

This appears to be by design but has become more obvious with the June patch. There is also a related report here on windows and curtains https://answers.ea.com/t5/Bug-Reports/NEEDS-INPUT-Curtains-no-longer-able-to-be-placed-on-angled-walls/m-p/9170089#M133257

Product: The Sims 4
Platform:PC
Which language are you playing the game in? English
How often does the bug occur? Every time (100%)
What is your current game version number? 1.63.134.1020
What expansions, game packs, and stuff packs do you have installed? All Of them, the issue started post-Eco
Steps: How can we find the bug ourselves? Try and Put anything on a diagonal wall, and the tooltip states "Must be placed on a wall." This occurs in retail locations and Sim's Home. It happens in build mode with the tooltip popup, and the object is just 'redded out' in live mode. I have changed lots, lot types (Retail or Home), restarted the game, and it still occurs.
What happens when the bug occurs? Items cannot be placed on Diagonal Walls, and Diagonal Walls are not being counted as walls. Objects placed on the wall on previous patches still work (ex: Retail paintings sold, lights turned on/off) but if they are moved off the wall they cannot be put back, and no new objects can be placed there. This is for existing diagonal walls and for any that are newly created. The same objects and items work fine on non-diagonal walls.
What do you expect to see? I expect tool tip does not state a wall is not a wall, and I expect the objects to go on a diagonal wall just as they would a 'normal' wall.
Have you installed any customization with the game, e.g. Custom Content or Mods? Never used.
Did this issue appear after a specific patch or change you made to your system? Yes
Please describe the patch or change you made. New Eco Patch, just downloaded the expansion today.

‌

Diagonals Walls no Longer Working

See attached for 3 Situations: Item Works on Flat Wall, Item does not work On Diagonal Wall, and Item Does not work and the wall is not considered a wall in build mode. Also seen is a light put there previously still working. The light, if removed, can no longer go on the wall, however. 

After doing some experimenting, I can say this:

This bug is consistent for me. It happens on every lot.

It happens with or without MOO on. I first noticed it when dropping the walls to play the game in my main house, and I only turn MOO on to do some creative plant placement. Like I said before, I can still get things on the walls with MOO on, they just never disappear when I cut the walls away anymore.

It does not affect windows or doors, just stuff like shelves, art, or wall decorations.

The main house I play in only has a few internal diagonal walls, and all but one of them is only one square, so this took a while to figure out, but what is actually happening in my game in the scenario other people in this thread are experiencing. The game is snapping objects to place in between squares on diagonal walls, and I only figured it out after fiddling with a longer wall. I have two screen shots of the same wall, one with walls up and one with walls down to show that an object placed in between squares disappears when I cut the walls away, but the stuff on the other side of the wall that was placed on the squares hangs in mid air. I also am including a series of screenshots where I moved to an empty lot and made a diagonal wall, and then showed how doors and windows place normally, but shelves only lock to in between squares, then I placed one with MOO and dropped to wall to show how it remains visible. (I'll put the other screen shots in a second post)

This problem remained after repairing my game.

My issue is that I have a bunch of single square diagonal walls in my lot that I made because I liked the look of cutting off corners, and previous to this update, I could decorate them without issue, and now I cannot decorate them how I used to without the stuff hanging around when I move to Cut Away mode, which is how I tend to play the game. If this is how stuff works with diagonal walls right now, it's really annoying for all my hallways, lol.

This is just three more screenshots showing how shelves interact with walls now. Notice how a shelf placed with MOO doesn't disappear with the rest of the stuff on those walls.

@SheriGR My walls are short, but I was able to place art that fit on a single square on them prior to the last update, now I can't anymore. I didn't use MOO to get the art I have on my single square walls originally, but now if I pick up the art I had previously placed there, I can't put it back down in the same square.

@Iamflare I feel your pain. I have a home with a diagonal section where I had previously placed art that was staying just fine when placed (I meticulously play and placement test my builds), and now as you can see the art is deleted when the home is placed. This also happened on the regular wall adjacent to it. I suspect this is due them being close to the wall edge. I also see that where I had 'debug blank canvases' as blinds on those windows (it's a starter), those seem to have been deleted as well. 

Before patch:

After patch:

On the other hand, the photo (and light) I had placed on the opposite diagonal wall placed just fine before and after the patch:

I agree with @Bluebellflora that this is probably by design. 
I'm assuming the wall placement dynamics have adjusted to allow for the new 'free placement' of windows and doors. <sigh>