It does look a little like the opposite of "bromide drag" to me. This looks like a streak of extra development, which would indicate the bromide is everywhere BUT the streak.
You say the streak was always in the pyro developed negs and in the same place? Such streaks usually depend on the subject matter, and should be in different places for different subjects. This is indeed a puzzle.
I have not found agitation schedule to be as much a problem as some others have when I use PMK or Pyrocat HD or any of my own staining developers. I do not use "gentle" agitation, however. The purpose of agitation is to get a uniform mixture of developer constitiuents including oxidation products. If you don't want that, don't agitate. At least that is my advice to myself.