I have a Rohloff equipped Surly ECR which I've had for four years now. I don't keep a track of the mileage but the Speedhub's oil was replaced in May 2018 and I recently decided to do it again, along with several other jobs.
One of the jobs was to heat shrink sleeve the two twist shift cables together which meant removing the EX cable box in order to thread the cables through the sleeving. However, when I tried to reattach and loop the cables around the pulley that lives inside the box; I couldn't. One of the cables was shorter than the other and when I pulled the inner's out, I noticed that along most of their length there were kinks & curls. I've no idea how/when this happened but I ordered some replacements.
The bike was put back together and I've probably done about 100k since.
What's immediately noticeable is that the shifting is now very light. For the last four years I've thought that this was normal "Rohloff" but that's not the case

There's also a noticeable roughness/rumble that you can feel through the pedals under load

BB?
I've double checked and it (a UN-55) which spins fine and there's no lateral movement. The tapers are have been cleaned again are grease free.
Pedals
They're new(ish) as the original ones died. They're also well secured to the crank arms.
Chainring?
Tightly held to the crank arm.
Chain?
According to my Park tool it's f**ked... The 0.75 gauge drops cleanly through, but does it matter if I don't have a derailleur? The flanks of the sprocket are no longer symmetrical, so I should probably replace the chain and spin the sprocket around.
I also read somewhere that it could be “chordal action” which should go after lubrication – no luck with that!
Chain tension?
The rumble is definitely worse if it’s slack but I have to tighten the tensioner all the way in now which I’ve never had to before.
Hub?
There’s no sign of leakage following the oil change but there was quite a bit of sludge in the old oil, so maybe it was this that was generating resistance internally and is why I was had to ride in lower gears? Could it be that this thicker oil was cushioning the vibrations that I’m now feeling?
Any ideas?