Tracks longer than 15 minutes — usually a Let's Play episode, a full album rip, or a DJ mix that slipped past the download-time checks — plus tracks Navidrome lists at exactly 0:00, which usually means it failed to read the file's duration at all (a truncated or corrupt download). Whitelist a track to keep it and stop it showing up here again, or remove it to delete it from Navidrome entirely and stop it from ever being downloaded again.