As reported by the Global Offensive subreddit (via PCGamesN), it appears that some new Steam Workshop submissions may require moderator approval before going live.
This screenshot from user TanookiSuit3 shows a banner indicating approval is required.
“Moderators need to approve the latest version of this item before it will be visible to other players in the Workshop.”
According to PCGamesN, Valve says this approval should take less than a day, and thus should not really be a major hurdle for content creators to get their submissions live within the Workshop.
