So, this only happened once, but it was so weird that I honestly want to know how and why this happened.
I'm making this as detailed as I can, because it happened months ago, but I do remember what happened.

I had placed a Maxis lot (Cape Cod Classic) in a custom neighbourhood of mine to place a family I would make. Then I went into Create-A-Family in order to make that family. Once it loaded, I saw for a split second what SEEMED like an adult female bald mannequin Sim spinning in an H&M polka dot dress (The yellow one), with her hands on her hips. At first I thought it was a teen female, but that outfit isn't available for them. I'm not 100% sure, because I only saw that Sim for a split second, because then the camera panned to OUTSIDE the CAS lot like you would place your cursor on the edge of the screen, and it would scroll to that direction. It threw me in the grass and I couldn't even see anything else. I could click the buttons to create my Sim and all, but it wouldn't zoom in or anything for that matter. I really don't know WHERE the Sim was, and Sims can't be randomized in the mannequin skin colour, so that mannequin was definitely not the actual Sim you create. Out of my horror I couldn't take screenshots (And I didn't know how, PrtScn alone didn't work ) and cancelled the family. Then something ELSE happened! Those plumbobs that hover over occupied lots were scattered and they didn't match the lot (Other plumbobs were even hovering on nothing!) or even if a plumbob did hover over a lot, if you were to place your cursor on the lot to see the family's name it would pop up on the other side of the screen. I went back to CAS out of curiosity and saw that now you were in the Studio Family Portrait Room (Or however it's called) and not the actual "Creating" room. Said randomized Sim that pops up once you enter CAS was peacefully standing like Sims in CAS would normally stand like, but weirdly, I think they were faceless?? I even remember how the Sim was! Skin 4, male, had this outfit , had this Mansion and Gardens hair , but had no face. I could click Step 3 to zoom in on his face, but I don't remember which face template he had! I cancelled the family and went back to neighbourhood view, again, same thing with the mismatched lots. I quit the game and restarted it, and everything was back to normal.

I swear, this may sound like a Creepypasta, but I'm saying the truth. I was as dumbfounded as you may be! I've never had this happen to me before, and this was the only time this happened. This hasn't happened to me since. I think it's also important to say that I didn't have CC installed yet, so a completely vanilla game, no mods, no anything user made. I also did not have TestingCheats enabled to see if some kind of Object Error popped up. (After that happened I learnt to always have it on incase something weird happens again ) The ONLY footage I've got close to this is one of CrystalFlame360's videos: Here (Timestamp: 16:01) but then again isn't exactly the same thing (Camera panned to the opposite direction forward, Sim wasn't even there.) Also, I think bald Sims can't be randomized in CAS? That weird glitch happened immediately, so I didn't intervene anywhere to say that I equipped that hairstyle on the Sim. That Sim could have been suffering from a jump-bug as I didn't have TestingCheats on, but Sims that jump when they have jump-bugs do it in a very sharp and immediate way, that mannequin Sim was spinning smoothly like you would spin a Sim in Bodyshop.

Please, if ANYONE knows what went wrong (I'm seriously dying to know! ), even if you aren't so sure, tell me!

Edit: I forgot to mention that I even checked the CASCamera.txt file in my game files to see if it was modified just to solve that camera panning bug, but nothing was modified!

Had you been drinking, or under the influence of any narcotic substances? If not then it sounds like either your game install/ userdata was messed up, or else this was a game glitch that was later patched out.

No, I don't drink nor do anything of that matter ! My game is patched, and I haven't reinstalled since then so I don't know what else that had to be.

I can't tell you why this happened, but it sounds like you may have encountered one of the Fashion Show Tester debug objects. The only connections I can make are the fact that CAS is technically a hidden lot in and of itself, so if something got weird with the lot ID numbers when you placed the new lot, it's theoretically possible for funky results to occur... but obviously that doesn't explain how that would happen, let alone if/how/why it would result in these particular events, or if there were other factors at play... Very strange.

This could be the only explanation! I swear this is the weirdest thing that has happened to me in the Sims! I wasn't messing with custom CAS lots either, I don't know what else it could've been. I didn't think of that hidden fashion show tester object, but it's really the only explanation for the smooth spinning and not the "laggy" one!

I had seen this happen with Calipers and Tongs' video, I think it was in the one with dying in CAS? I can't make any connections between Crystalflame360's video, Calipers And Tongs' video, and my case, though.