My bike is equipped with a Shimano Alfine 8 (SG-S7001-8) hub. It runs smoothly without significant noises and shifts up and down easily, except down from 5 to 4.
When I try to downshift from 5 to 4, it has difficulty engaging the 4th gear, simply remaining in 5th. When the problem started, it only happened occasionally, but it got worse over the last couple of months. By now, the 4th gear engages about once every 10 attempts. It makes no difference if I stop pedaling or keep applying a light load.
Of course I checked the adjustment. Initially the yellow marks were slightly off, but they are nicely aligned now and the problem persists. I also tried setting the cable tension a little bit higher and lower than indicated by the yellow marks, but to no avail.
What can I do?
Update: I tried Criggie's suggestion to try different adjustments, a bit further before or after the yellow mark. It didn't help unfortunately.