@Graeme-3,
Also the distance between the waypoints is almost 20km. That leaves A LOT of interpretation for routing to the navigation settings. It is best to have waypoints each 1 to 5 km depending on the kind of roads in your route, and of course to use the same map in the route-planner (which is Here if you are using MRA Navigation). But even when using the same map, navigation over 20km can be off dramatically of the navigation settings are unequal. I make it best practice to never touch the navigation settings, but place enough waypoints to to guarantee the correct route. The navigation settings in MRA Navigator jump to defaults each time you load a route anyway, so it is nu use for detailed routing.
Some time ago I have put an idea in the "good idea's box" to have the navigation settings be part of the route-file. That will guarantee that navigation settings you set in the planner will be loaded in MRA Navigation for each route independently. But I have no idea if that will be picked up.