I cannot wrap my head around the issue I'm having and after days of trying to fix it I've had maybe 10% luck today then back to 0. Ever since I downloaded a couple gallery pose packs made by Vanderetro on 11/22, I've been having issues with all of my Household thumbnails changing to look like the pictures attached.

I've tried everything. I've tried first to remove the pose packs because I ended up not liking how they turned out in my gallery, not realizing it changed all of my households within the game. So then I tried removing my poses folder from the Mods folder and it didn't work. Today I tried Removing all of my cc and then removed the text documents so that the game could regenerate them and load as new. The poses were gone then. But then I tried to do my usual 50/50 cc check (I have everything neatly sorted so that it's not too difficult). Well each folder I added caused my game to do the weird funky thumbnail poses again. Almost as if every one of my cc are corrupted or something. I then tried to just delete the localthumbcache file and the thumbnails seemed to reset correctly, but after I went into CAS to fix one of my family's appearance from yesterday's update the weird poses came back again!!! ( I've also tried multiple time to repair game in Origin that never works for me for any issue I ever have)

Is there anything I've missed trying that I'm not doing? I have the game downloaded on two different computers with the same issue. I also forgot to mention that I have also reinstalled my game twice. I've also used sims 4 studio to repair some of my cc. My head hurts from this and I feel it's something simple like a file overwrite or something but I cannot for anything figure it out.

Did you replace your TS4 folder and let the game generate a new one?

Even when uninstalling and reinstalling the game, the TS4 folder does not get removed because it has your Saves, Mods and Tray folders inside.

1. Make a backup of TS4 folder.
2. Delete original.
3. Start game. It will build a completely new, glitch-free TS4 folder.
4. Quit game
5. From your backup, place mods, saves and tray folder files back. (Mods that you know to be updated and safe.) Also put your Options.ini file and UserSettings file back if you wish the game to be set up the way you like.
6. Start game and see if this has nuked the unwanted thumbnail effects. My guess is they'll be thoroughly gone.

I've tried similar that. I deleted everything and removed all of my saves tray files and mods. When I ran the game "fresh" it was fine but once I added everything back the glitch returned.

Also what I meant by checking the mods, I would but one in the folder to test and the poses would be in the thumbnails, so I would then remove it and add another one to test. No matter what the poses would reappear so testing my cc to find the culprit is impossible.
I will attempt to just completely remove the entire sims 4 folder and let it regenerate everything as you suggested and check back.

Ok just tried it. Added one cc shirt to test it after Running it with absolutely nothing, and it did it again. I don't understand how that one pose pack I downloaded a month ago has messed up all of my other CCs