I have completed the main quest line. I have done 62 jobs for the Thieves Guild, consecutively, over the course of a few (real life) days, little by little. I have done a variety of jobs from both Vex and Devlin, and I have been given and completed THREE of the FOUR special jobs. Not a single one of my 62 jobs has been in Windhelm, and as such, that is the last remaining "special" job (Summerset Shadows), according to the wiki.
What do I do? Do I have to do something specific in Windhelm to begin getting jobs there? If I'm bugged, how do I get the achievement?
My version number is 18.104.22.168.4, and this is on the PC.
EDIT: Well, I've been doing it for about 2 hours since making this question. There's simply no way my luck is that bad --- the game will simply not give me Windhelm jobs. The only thing special about Windhelm is that I captured it (as I sided with the Imperials) as part of the Imperial questline.