Hello,
NCN1 seems a bit odd at https://www.openstreetmap.org/relation/15978999#map=19/52.962852/-0.021894 .  It turns off the main road and then stops.  There's a footpath that continues north, but that isn't tagged as allowing cycle access.  Then the cycle route continues on the main road.
Further north https://www.openstreetmap.org/relation/15978999#map=19/52.964399/-0.022771 there are another couple of odd gaps?
To look for gaps you can use https://ra.osmsurround.org/analyzeMap?relationId=15978999 and then zoom in.
Best Regards,
Andy
