Currently I have some highway=footpath or highway=path or highway=track around me that have mtb:scale=* or mtb:scale:imba=* values but are not associated with any biking sport so they don't show up on your site when I select Biking Trails or Mountain Biking Trails....unless I select "All Trails".
I know generally we should be logging into OpenStreetMaps and correcting issues for others, that's not always a quick thing to do though. So my proposal is to add an option to automatically classify any highway=footpath or highway=path that has a mtb:scale or mtb:scale:imba value as a bicycle and mountain bike route and have it show up when selecting one of those activities from the dropdown.
Thanks! Keep up the great work!