This is an error which mainly occurs with Firefox on Windows 10. As soon as a gpx track of a tour whose title contains special characters is downloaded, Firefox shortens the title up to the first special character and does not adopt the file suffix “.gpx”. This is the reason why the gpx file is not recognized as such by the computer and some gps devices.
Solution: Please use Chrome for downloading a gpx track. This browser recognized the special characters and automatically creates the suffix “.gpx”.