@lavagoddesss When you go into Buy mode, there's a button that lets you sort items by the pack they came with. Are all your packs listed? If not, the launcher may be unchecking packs from the installed content tab, or it may be ignoring your selection. The solution is simply to restart your computer, uncheck all the tabs, and then recheck them. This is definitely tedious, but the launcher is finicky like that.
If your custom content is in your game folder (from your comment, I'm not sure what steps you've taken up to this point), just make sure to delete your cache files. They should be cleared regularly anyway, and every time you add or remove content from your game folder. For reference, they are:
- CASPartCache.package
- compositorCache.package
- scriptCache.package
- simCompositorCache.package
- socialCache.package
If this doesn't help, or I'm misunderstanding the nature of the problem, please let me know, and I'll try to help.