Privilege banner buggy? Or am I just confused?
I got a congrats message for a privilege I have not yet earned. I am 1 point short of gaining this privilege. Is this a bug?
The mechanism that awards privileges is not 100% in-sync with your actual reputation score. There are processes that run every few hours to recalculate privileges and badges earned, based on your reputation.
It's possible that your reputation was momentarily above the threshold for the privilege recalculation process to run, but then afterwards your reputation was reduced by some other event that took place in the system (such as downvotes, someone taking back an upvote, someone accepting an answer and then unaccepting your answer, etc.).
However, even though the banner notifications aren't in sync, the actual privileges are. For instance, the moment I was above 1000 reputation here, I could see vote counts on questions and answers, but the actual notification that I had earned this privilege didn't happen for a few more hours.