Hi William - Thanks for flagging this up, we'll report the issue to Google. In the meantime you can either set set the Auto-Plot switch to "Off" and plot manually along this stretch or use the Paths map with the Auto-Plot switch set to "On Foot", which seems to work.
John
Malfunction persisting to date
The system appears unable to complete a road plot through the dog-leg bend to the south of Swar Beck on the Grinton to Leyburn road in North Yorkshire UK at approx 54.368032N 1.927092W.