This issue has been there since the start of the game, so maybe a bug report exists somewhere already.
For multiple wall patters that have this vertical edge part, it is not applied correctly on corners when the wall is only 1 piece wide. I would expect it on all outer corners.
As you can see on my house here, it does work as intended on the first floor but not on the bottom floor on either side of the door.
From the other angle one white piece is applied on an inner corner but only on the right side, not the left side
here is another example
This has always bugged me! It's inconsistent no matter how you place the wall pattern by whole room or single tile the edging always goes wonky 🙄
I wish they would give us decals to place on both inner and outer corners and call it a day. I never use those wallpapers because the corners never align right.
I see my post got moved to feedback and ideas, but I found the bug report on it:
https://forums.ea.com/idea/the-sims-4-bug-reports-en/certain-wall-swatches-dont-display-corner-accents-properly/12501672
I've noticed this too. I sometimes use a basic square column instead of those wallpapers so I can add vertical wall trims to the exterior of the house myself and line them up properly. It needs the move objects cheat in some instances, but I'm a bit happier with the aesthetics. I wish they could reach to the foundation level though...which is another pet peeve!
It would be nice if it could work similarly to floor tiles where the alt key can place the corner item. Most of the time we get a swatch without them too. Even with floor patterns cutting it up fixes 90% of design issues.
