Even experienced cyclist find some of the route horrible
NCN21 at Woldingham golf club is a downhill mud/cobbled bridle path, chewed up by horses and entirely unfit for purpose. I found that out in white sidis on fancy wheels and haven’t trusted an NCN since.
I had similar near Llandrindod Wells, went back to work & spoke to the NCN team to politely suggest they make it clearer on signs that muddy stuff would be in store long the route. They weren't interested.
Even experienced cyclist find some of the route horrible, like there’s route go on the 60mph A road for several miles.
The failing is on Sustrans themselves not rectifying this for decades.