Hi!
I think this is a false positive when the way is a sidewalk or footpath. stop_position is for ways on which the bus drive. In the Quebec province, we are snapping most bus stops to the sidewalks, footpaths or cycleways with foot=designated or foot=yes used as sidewalks alongside the bus stop sign so routing engines can bring you to the actual stop location where you can board/alight the bus. This should not trigger an error in osmose.
Thanks!