See the route at http://cycle.travel/map/journey/13541
In two places, the route description says "Continue on (unnamed route)" for a short section. Both cases correspond to a section of road that has an adjacent parking area, where the OSM data has the car-park boundary sharing nodes with the road. I presume C.T is routing through the car-park in preference to the road, and thus not finding a road name.
While I'm not sure the data is 100% correct (the car park doesn't go to the road centreline) it's probably a reasonable representation of the fact that the car-park is open to the road along a finite length. I think this representation is used fairly frequently in OSM, so probably C.T should probably try to handle this situation a bit better.