Your best bet would be to contact Just Trains support and they can look into this for you.
South of Frankfurt Süd and Stressmannallee, there’s a 30km track leading down to Darmstadt(?) which seems to be the S3/S4 line between the two stations, this track has absolutely no scenery for some reason. However, station markers are present up to Neu Isenburg. Does anyone know why this is there?