Workshop Forced Re-downloads

[JurisDocta]

All of a Sudden Steam starts re-downloading my mod collection for certain games (Stellaris, X-COM 2, and Star Ruler 2. What can I do about this because trying the solutions for the "Game appears as Uninstalled" isn't working. Is there a command I can do and if so how?

Edit: I should mention that my workshop content is all there.

[VVizard]

Also having this problem. I have tried most of the solutions a quick google search will present, but nothing has worked. I tried scouring Steam Support, and nothing is relevant. I can locate all my workshop files on disk, yet nearly every time I open Steam it starts up the same 42.9GB download of my Arma 3 mods, as well as any other games it seemingly randomly lumps in.
My only clue as to why this happens is that all of the games are on my second hard drive (most of my games are on there), which has been having issues with not reading after an arbitrary length of time using my PC. It fixes on restart, but it isn't always a precursor to the download issue: sometimes it just decides to redownload my subscribed workshop content on its own regardless of whether the drive works or not.
I got fed up with it redownloading a small batch of Dominions 5 mods today (5 times, 5!) and suspended all workshop downloads. As a result, it "uninstalled" all the games I suspended. I use quotes because when I pressed install for the aforementioned Dominions 5 (500ish MB) it detected the files and instantly installed. I tried this with the substantially larger Arma 3, but that was trying to take a ludicrous amount of time to detect the existing files so I canceled it for now.
The previous paragraph leads me to believe that the problem is on Steam's end rather than my PC's, however I will not stop searching for workarounds I could implement on my end until they (probably don't) do anything about this. I am not sure why it won't detect the workshop content which is clearly in the install folder, but will detect the game's common folder and skip the download there.

Any fixes or advice would be appreciated.