So I'm looking at the wiki article, and it I notice that when they create the container for the leaderstat objects that the container is named leaderstats. So I tried using the leaderboard with the container named leaderstats and it worked, but when I renamed the container to something like Leaderboard, the stats stopped showing up in the leaderboard.
Does the container have to be named leaderstats?
As evidenced by your own tinkering, the answer is yes.
The reason for your downvote is most people would assume that it follows that changing the name to something other than "leaderstats" causing the leaderboard to disappear means that the container has to be named "leaderstats".