A user visiting https://en.wikipedia.org/wiki/Special:Log
is able to see a record of when a user hides or unhides a collection.
In pulldown:
hiding collection
unhiding collection
In Special:Log you should see:
timestamp | hyperlinked user (talk|contribs|block) | action | hyperlinked "collection" name | author name | (action summary/comment or MediaWiki reason for action if we have a dropdown) | (admin action option) where the admin action option would be (view|restore)