A few weeks ago I rode a route that I have done many times.
on this occasion the NN did exactly as you describe here. tried to send me off and back on the motorway at almost every junction.
I had 1 start point 400m away from my house and the next shaping point was located at the end of the motorway section. I did not need anymore as I know the route, it was a means of getting to the twisty toads and these two points were circa 50miles (80KM) apart. only reason I had the two initial points was to give me a rough arrival time. route as track
I sent the log files to the devs, did not get an explanation, which I wasn't really looking for, the answer I received was, they would use the findings from the log files to help with updates. which was my intention when I sent the log files.
curiouser and curiouser