Is it just me?

@ZeldaPrissy Is this possibly what you're seeing? If so, you can add your information and 'Me Too' and follow that bug report to see if a solution/work-around or fix comes...
https://answers.ea.com/t5/Bug-Reports/OPEN-SD-Missing-nails-in-CAS/td-p/12489099

@ZeldaPrissy If you read through the nails bug report there seems to be several potential issues, including one where there was a swatch change. Is it possible that you are seeing a nail be removed that was changed in an update? 

Can you share a screenshot of the item that is missing in BB that you noticed was gone? 

There is a bug report about getting a message that items were removed and nothing is missing: https://answers.ea.com/t5/Bug-Reports/NEEDS-SAVE-Items-Removed-pop-up-appears-when-no-items-removed/m-p/10526256
I just chatted with a friend who says he has gotten this message on every lot recently. Edit: this same friend also went in and checked, and he says some of the nails are missing from the selection panel for these Sims. He just checked and the Sim still had the nails on, and the nails seemed to stay on the Sim if he leaves them alone, but if he removes the nails there is no option to put them back on, and there is no ability to change their color. There is a bug report about this here: https://answers.ea.com/t5/Bug-Reports/OPEN-SD-Missing-nails-in-CAS/m-p/12489099#M247956

If that bug report matches that part of your issue, you can add your 'Me Too' and 'XP' to the report and follow updates on it to get notified if people share any discovered workarounds or if there is a solution in a patch.

It's also possible you have a couple of these things going on and that's making it even more confusing? 🤷🏽‍♀️

The green checkmarks are ones that are available for use, the red marker is the one missing and is nowhere to be seen in the nail category or even in the accessories in general. (note that the nails were only on my sim because I had it saved in my gallery, its matte but I chose a different swatch)

I also had this problem in the build and buy as well. The gaming chair I also use frequently had disappeared out of the blue.

@ZeldaPrissy Thank you for the screenshots, they were very helpful. I have a couple of additional things to ask after seeing these screenshots...

• I see that you are playing with CC. Have you tested to see if any of these issues are gone if you remove the the Mods folder to your desktop, and the cache file as directed in the spoiler tag?
  
  Spoiler

  Exit the game. Move the Mods folder from your "The Sims 4" folder [Documents > Electronic Arts > The Sims 4] to your desktop (save it for reference) and delete the localthumbcache.package file in your “The Sims 4” folder. Then check in a new game save to see if this issue is still occurring. You can then test without saving – or in a new vanilla game save – in order to identify which CC/Mods are causing the issue. Then remove or add updated version(s) of the Mod/CC causing the issue.
• The 'removed items' message you sent a screenshot of mentions that you may not own the item removed &/or that you may not be logged into the player account that owns the item. Could either of these things be the case for you?
• I also found this Bug Report about the 'Vibing Streamer Gear Digital Content', which appears to include the chair you're missing: https://answers.ea.com/t5/Technical-Issues-PC/I-didn-t-get-the-Vibing-Streamer-Gear-Digital-Content/m-p/11672985#M235622

I removed the mods/cc and the issue is still there, while I even tried logging out and back into my account and the problem still lingers, I own many dlc's, not all of them but many. High School Years is one of them as well as Spa Day

Actually, I just now came across something new.. When I play ts4 I usually use cheats (whether money or family) I had this option to choose expansion pack cheats and this was what I saw, I had more packs then that.. I hope this helps..

@ZeldaPrissy Thank you for that information and testing with the Mods/CC removed. Were you able to read through the links to the potentially related issues in the message above - message #4? I was wondering if you noticed that I edited into that post the information my friend saw when testing this in his game with his Sims (he is also the one who was getting the message about removed items). We were wondering if you could confirm if this is the same as what you are seeing in your game in regards to the nails.

The screenshot you just sent is apparently function added by a Mod.

So since the time you purchased the high school pack and had the bonus content from it in your game, has there been any change in what computer your game is loaded on?

Is the the account you purchased and downloaded the 'early order' through/on the same account you're using now?

to your last question, yes I'm using the same account, as for the second to last question, I'm not sure if I understand. Currently I removed all of my mods so the screenshot was the cheats option which I assume is used for the base game including dlcs. For the build and buy, I was confused the entire time, I just purchased the High School Years pack, and the gaming chair, wireless speaker and LED panels just automatically came with it. I don't know whether I had to purchase those things as well.