weird. Exactly at the position where your marker is? So only the part that goes to house number 51f? And the part of the street before, houses 53 and 51a are still reachable?
I cannot believe this, do you have a photo? I will map it now but it is really weird. Look at https://www.tim-online.nrw.de/tim-online2/. This is the official "Liegenschaftskataster". It is white area (german: "öffentliche Verkehrsfläche" - so a public street). Pink would be private. And it has a street name. And it is a connection to the train station. The post man must reach these houses shouldn't he? Either NRW Atlas is old and something has changed or we have found a house owner who is blocking the road illegally ;)