@Corjan-Meijerink
Thank you for the immediate response. I understand that MRA depends on the accurancy and up-to-date information of Here maps, which - IMO - is very poor, as described.
I think I have found and will evaluate the solution of a competitor that - at least on the first look and also at an affordable price - appears as if it fulfills my most important user needs:
motorcycle optimized route planning
maps updated by an active user community
web site tour planning and Android app for navigation
Android app allows to report road blocks and do a detour
management of my planned tours.
I will continue to use MRA for my car routes, but it seems I will switch to another solution for my motorcycle tour planning and navigation.