Where and when are you seeing this? Based on the info you’ve given so far, I would guess that it’s referring to mods from the Steam workshop. My initial impression is that this is a Steam issue, so the help you receive here may be limited. It’s been at least a year that I ran any significant number of mods on a game, but if I remember correctly, getting them to actually uninstall through Steam was quite a pain in the butt. I don’t remember what I had to do, but I remember having to jump through several hoops to get it sorted.
It’s the mod content, as far as I understand. I have seen Steam “downloading” patches of 0 bytes for the Workshop content for a couple of games recently, not just Conan Exiles.
So as @bbtech says, it’s probably a Steam-related issue rather than Conan Exiles related.
My internet connection is dog slow, like 3 Mbps max download. So getting these Workshop Updates out of the blue really takes the cake.
If I simply restart the game client, and there’s a Workshop Update waiting for me, I’m stuck waiting 5 - 50 minutes before I can get back into the game. Super annoying.