Hi Bonnie,
Yes, I've had this issue before. It is documented in another thread - I think you need to look in the technical issues threads.
It basically has something to do with the size of the files of CC/store bought content. If you attempt to upload/install a file larger than the limit on the size, Sims 3 basically goes, that's too big for me to handle, so I just won't install any of them. This is a limit due to the technology available at the time of Sims 3, and I don't think there's a way around it.
A spreadsheet has been put together by someone who has a recommended order in which to reinstall the CC/store content and which ones to put together to get the CC/store content 'to remain saved.' On a laptop at the moment, and away from my gaming computer, so I can't be more specific than that, sorry
MrsFlynn along with some others helped with this. MrsFlynn may be able to provide better assistance than me.
Edited to add:
These links may be of assistance to you as well.
Sims 3 - How-To: Fix Problems with Mods/CC
https://www.carls-sims-4-guide.com/forum/index.php?topic=31759.0and
Get Store Content Recognized By Game
https://www.carls-sims-4-guide.com/forum/index.php?topic=31649.0