I noticed that I have just been granted "Steward" badges a second time:
I guess that is a bug that should be fixed.
Edit: for the record – this has been fixed.
The rules are being changed; you're getting one Steward badge for every 1,000 reviews in a queue. See this comment by Stack Exchange staff member @animuson:
There's supposedly an announcement about review updates coming out today, if it hasn't been published somewhere yet. Seems the code is getting ahead of itself.
However, there seems to be a bug:
This is my bug, caused by a temporary issue with and old batch job running after a migration took place. I have a fix I can roll out in a few.