Yes, something has changed, but you won't see it... yet.
I'm working on implementing a monthly leaderboard, and it's a bit more complicated than it seems. This is because I don't want results older than a month to be taken into account, and this is something that Steam's leaderboards don't offer out of the box. So I'm testing a possible implementation...
The solution I'm currently testing has the game clients save their score on a daily hidden leaderboard. Meanwhile, the game server runs a script every 10 minutes that deletes daily leaderboards older than 30 days. Then takes all the results from the remaining ones and adds them up into a global public leaderboard. This creates a "sliding window" for the results of the past month only.
If all goes well, the next update will reveal the whole new leaderboard in all of its glory :)