I just saw a new badge notification:
You've earned the "Mortarboard" badge (Earn at least 200 reputation (the daily maximum) in a single day).
But I am nowhere near 200 rep this day (only +30 rep, no bounties or whatever at least I am not aware of) not even in combination with other SE sites.
After some digging I found:
Awarded Nov 19 '18 at 22:50
which was more or less exactly year ago so it looks like its just a glitch in notification system.