@DavidF This is really weird, there shouldn't be anything different between Grbl 1.1e and Grbl 1.1f that would cause jerkiness. I think the motion planner is the same code.
Is the actual output different, can you visibly see it or is it just acceleration / deceleration on the vectors that is making it appear jerky? That may just be Grbl parameters, although using my send defaults should have made them identical.
I'm not sure what else to try at this point, perhaps compile the latest Grbl 1.1 release with Z-XY homing enabled.