So, after a certain number of Mods are downloaded, I get the "Operation unable to complete at this time" message when I attempt to download more.
Now, if I delete a mod or two I can then download a mod or two, but then no more... so it seems on PS4 at least that I've hit the max number of mods I can install. But I still have 800 MB of free space for mods according to Skyrim. Wth?