I love planning cycling routes on openrouteservice since it handles large amounts of vias very well.
I noticed that the routing often deviates from the obvious route though.
Not sure if it depends on the weighting or on errors in the OSM data, i looked at the data via https://www.openstreetmap.org/edit#map=17/51.32918/6.97519
but could not find any obvious errors (not experienced with mapping)
An example of what i mean: