Missing CS:S Content

So about a week ago I was playing on my Trouble in Terrorist Town server and everything was perfectly normal. However, when I logged back in the next day, all of the CS:S textures and models were missing completely. Also, I am unable to download any sort of custom map due to the “Map _____ missing, disconnecting” error. I have absolutely no idea what could have caused this issue. Before you ask, these are the things I have done (none worked):

-Verified game content
-Made sure “Allow all custom files from server” is enabled
-Made sure CS:S content is mounted (triple checked)
-Deleted Garry’s Mod folder
-Reinstalled Garry’s Mod
-Deleted ClientRegistry.blob
-Countless of other obvious things like rebooting my computer and making sure I own CS:S on Steam

It would be simply fantastic if someone helped me out over here, since it’s an absolutely ridiculous issue.

Have you tried to re-install CS:S or launching the game again to make sure the files are there?

I do not have CS:S installed nor did I have it installed before. The CS:S files required for Gmod suddenly went missing. I will try installing it to see if it works, however.
Edit: It’s “Validating Steam cache files” when I try to install CS:S, I guess that could be the reason for the missing content. If not, then I will install it and play it to see if it works.

It works now; after Steam validated the CS:S cache files, the content was successfully mounted.