Today I saw that the Drafts label is missing in Gmail. I even went to Settings / Labels and made sure that it’s set to show always. It seems to be a bug. There’s a quick fix:
go to any other label, and you’ll see at the end of the location “#label/WHATEVER”, now just change “WHATEVER” to “draft” and hit enter.
Another solution is to search for “labelraft”
Update: Actually what’s even more annoying is that the Compose mail button disappeared too. It turned out that the bug happens only in Google Chrome. Embarrassing bug!