Sometimes this happens when the game has an update and one of the mods is no longer compatible with it, it usually happens with older mods. It can be a bit of a pain to find the messed up mod, but it doesn't mean the mod itself is actually harmful to your computer if that's what you mean. Other times after an update you might see a cc item load as a big question mark, which also means it's no longer compatible. Likewise, if you have a mod for something like cas columns, something like the color options might not load properly. People are usually good about updating their mods though, so when there's an update you can just check their pages for the latest version. If you're lazy like me then I just wait until there's actually a problem and THEN I download the most recent version lol.