Did you try renaming the column, so that it is not last, and see if it appears? Is it missing from extract only, i.e. can you see it if there is no extract?
After playing around with it a bit, it turns out to be a bit more complicated than I originally thought. First, it was only alphabetically last among dimensions. Second, I could only get it to work by renaming the column in custom SQL. The new name showed up, even though it too was alphabetically last. However, I was unable to alias the new column with the original name, because Tableau thought that the original column already existed.