The other day I posted an article about Google Play Game services and an issue I was having with the leaderboards. Happily I was able to solve the issue.
It turns out that if your Google+ profile is not public then your scores won’t appear in the leaderboards (which are also public). As soon as I made my profile public all of my scores appeared in the leaderboards.
Hopefully this information will help others who are struggling with the same issue.