To add - at least in the past (I haven't tried it recently) I didn't have any issues with Stellaris or HoI4 mods from Workshop, they worked instantly. I know there is a thread somewhere in the discussion about a procedure what to follow but issue is now that the downloads won't even start. I haven't been able to initiate a single mod download. However I still don't have everything what I have subscribed from the Workshop. Last night I had success with this method and I was able to download couple of mods. I have tried subscribing then restarting Steam in administrator mode - then unsubscribing and subscribing again and then waiting for few minutes. I have created 'mod' directory into my /documents/Paradox Interactive/Crusader Kings 2/ and I'm sure that I have read and write permissions there as well. If I restart Steam the download is gone and nothing happens. If it does initiate it, it shows up in downloads but doesn't progress at all. I have an issue when I subscribe a mod from Workshop it doesn't initiate the download.

Ck2 steam workshop not working