It was a shift-cable tension issue. I put the Alfine in 4th gear and adjusted the tension by the barrel-tensioner at the shifter module (on the handlebars). A little collar had to be lifted away from the module so the barrel could be turned and tightened (or loosened) as required. I made the tension-lines in the hub almost true but it was feeling a bit wonky at the barrel-tensioner so I stopped with them overlapping ~75%. Took it for a 7 km spin and it was shifting much more accurately in 4th to 6th gear. Very nice; again.