I was decided to read algebraic attacks and gave points as usual. I got the Suffrage badge. Vox Populi badge continued as I continue. It stuck at 39 and did not allow me to gave any points. Now, it was reset. I think there is a glitch somewhere.
I found the answer from meta.stackexchange
You only get 40 votes in a day if a sufficiently high ratio of your votes are on questions. If you vote on only answers, you'll run out after 30 votes.
The more questions you vote on, the more votes over 30 you'll get.
Bottom line: The Vox Populi badge requires you to vote on a lot of questions during the day you earn it.