Several affected users have reported that they were able to resolve the issue by opting out of every Beta program. The account is tied to Steam Beta – As it turns out, the frequency of cases where this problem occurs is higher with accounts that are enlisted to Steam Beta.In this case, you can fix the problem by clearing the download cache. Whenever this happens, the downloader will refuse to download any new items. Download Cache contains broken files – There’s also a fairly common glitch that might occur in situations where there are a lot of pending items inside the Download queue.In this case, you can resolve the issue by deleting the corrupted mods and do an integrity scan. If this is a widespread issue, Steam will eventually refuse to download any new mods.

If this scenario is applicable, you can verify if the mods are actually downloading by switching to Big Picture Mode.