We care about artists' rights! In-order to both verify your Spotify account details, and also upload your listening history back to Spotify, you must refresh the playlists on your Mighty at least once every 30 days. This is so Spotify knows how much to pay the artists on your playlists!
If you are hearing the audio message to re-sync your playlists, just re-connect your Mighty to the mobile app and refresh it's playlists in the 'Home' tab and you will be good to go for another 30 days. And make sure to refresh them again within the next 30 days if you want to avoid temporarily loosing access to the content on your Mighty.