I gained no reputation recently on meta, I've even lost 50 yesterday.
Still I just got the notification You've earned the "Mortarboard" badge with a link to my meta badges.
Here's what I see in https://meta.stackoverflow.com/reputation :
rep cap was reached via rep from upvotes only on 1 days
earned at least 200 reputation on 0 days
which seems a little fishy.
Had I had some activity recently I would have supposed I was voted then downvoted, or something like that, but as that's not the case, I conclude there might be some bug.