Mods are automatically deactivated when the game receives larger updates, because many mods will likely need compatibility updates. If you save your game while mods are off, any cc will be removed. Turning mods back on will put the cc back in the catalog, but it will have been removed from sims and lots.
It’s always best to test new updates & pack installs with mods off at first - either in a new save or in a single mod-free save you keep for such testing. Then you can carefully add mods back in, checking for updates and testing in batches. Once the cc is back in the game, then you can switch back to your modded save without losing anything.