GraphHopper add-on for Locus Map shows "No content"

I have encouraged my son to use Locus Map and OSM mapping on his Samsung 'phone running Android Nougat version 7. I use the GraphHopper add-on for Locus Map for my navigation. I installed the GH add-on .apk to his 'phone successfully. I have copied my own england-20170503.osm-gh data (folder containing seven files) created from a Geofabrik download to Locus/mapsVector on his 'phone, too, as I have done with updated routing data many times to my own Moto G 'phone running KitKat version 4.4. Yet his add-on states, “No content”. I have carried out the same procedure successfully to my wife’s Moto G 'phone, previously. I wonder where a problem might lie? I have tried the Locus Map forum already without success.