I'm running 10.14.6. I was looking through the calendars in Language & Region settings (such as Coptic, Hebrew, Persian, etc) just because I was curious to see what they looked like. Then I changed back to Gregorian (the default) and found that the month (in this case "Apr") was missing from the menu bar. I tried restarting but that didn't help. I also tried fiddling around some more in settings but it's still the same.
For some reason, this thing won't let me add the URL so I put a space between the h and the t.
h ttps://i.imgur.com/o0Ovonu.png