Struggling to get the chain to come back down the cassette properly. Goes up fine (small > big cog), but cannot adjust it to come down (big > small cog) properly without going too far the other way, and not being able to go back up.

Usually, I would assume sticking cables, but have Jagwire Racer Pros with only 300miles on, so wondering if it could be something else I should check?

Shimano 105 shifters and rear mech, for the record. Whole drivetrain has 300 miles on.

Is the cassette lock ring on tight? (does the cassette wobble much)

The only other thing I can thing is the mech hanger – does it index nicely at one end of the cassette, only to be out at the other end?

Cursory inspection suggests cassette is ok. Non-removeable mech hanger, as steel frame, and seems ok by eye.

Has it been a recent problem or something that has got progressively worse?

Is the upshift smooth and takes minimal effort?

I’ve had a similar problem previously which turned out to be a badly cut outer. There was a little tab left on the outer and the ferrule compressed it. Meant shifting into a larger sprocket was fine, but relying on the mech spring tension to pull the cable back through on when shifting to smaller sprockets was delayed and eventually didn’t work.

It seemed to start last night. Fine up to then. Can adjust so it upshifts nice, but even though downshifting moves the rear mech to what seems almost the right position, the chain doesn’t shift down.

Have just replaced the cable and outer, and it’s still doing it. It’s like somewhere there is stiction, but I’ll be buggered if I can see where.