In the same way that hiding a collection triggers a log, it should also trigger either an echo notification or email to a user so that they know something happened and have instructions for changing their content or appealing.
Message: Your collection was hidden. Collections are hidden if they go against our [terms of use| https://en.wikipedia.org/wiki/Wikipedia:Gather/Moderation_Criteria]. You can contest this [here | https://en.wikipedia.org/wiki/Wikipedia:Gather/User_Feedback]