Looks like a lot of people have this problem. Running Windows 10. tomtom connect installed (latest version, as have reinstalled just to be sure). All other issues working fine such as charging watch, syncing via the mobile to strava etc. - all good. However, I cannot get it to sync to playlists generated by windows media player. I'm ensuring they are m3u format and that it is searching in the root folder. I have checked they are in the root folder can play them in media player from there, and it works fine, but tomtom connect will not find them and so I cannot upload them to my watch.PLEASE do not post the same reply you post to all of the similar comments. I've tried all your suggestions. They're not working.
And I'm about to return my watch for a refund.
Look forward to hearing from you.