@SheriGRHi!
I'm playing on PC and own almost every pack, I only lack couple of Stuff packs (I don't own My First Pet, Romantic Garden and Perfect Patio).
Game version 1.60.54.1020
It has happened on multiple worlds previously, I really can't remember which all. The Honeydew lot in University at least. The latest one (yesterday) happened in Brindleton Bay on the left bottom corner lot. I can't remember if it once had a building on it (I put a pic of the lot, because I renamed it and am playing in Finnish so pic helps more I think), but right now I was building from scratch. If it happens again soon I'll screenshot something for you but right now I have none.
I had problems previously with that Honeydew lot also, not able to remove or build walls etc (and I have no idea what that "conflicting block cluster" means because as I said my game is in Finnish so ^^' ). But I had no error messages or anything this time, it just didn't recognize the walls when I tried to place wallpapers or use select tool to use the same wallpaper. Before restarting I didn't try removing walls so I can't say for sure if I had gotten a error message if I tried.
I haven't used mods for a looooong time, but I'll remove the cache files and use repair anyway just to be sure. If the problem reoccurs I'll be sure to tell.
@Sozki Thank you for your information and screenshot! I'm glad you're going to try clearing the cache per the directions. Sometimes this can cause issues related to a broken Mod/CC even after the offending Mod/CC has been removed. Doing the game repair afterward should also give your game files a good check and repair if needed, in case anything in them has become glitchy or corrupted. That's a great place to begin troubleshooting.
If the issue does reoccur please do try to capture screenshots, as this often helps a great deal. If it happens on a particular lot you could also save and upload the lot to the gallery with a name something like 'Glitch Test', and let me know it's there, and I could test it in my game in the same lot. (Please include what world and lot it was placed in and your gallery name if it's different than on AHQ.)
I look forward to updates. Hopefully it will be good news that clearing the cache files and doing the repair fixed the issue. If not, we can try a game reset &/or the above lot share via the gallery.
