If you’ve downloaded music tracks from a video source, there is a chance that your software did not pass the correct parameters to the audio converter. This is the case with a certain Firefox extension YT downloader that passes the files to ffmpeg. The music track contains extra space for the non-existent video and the track time is twice as long. iTunes/Music.app has a bug where it will play the next track during this blank time, therefore, the CoverArt and Title will not change while the next song plays. You will need to reattempt to convert the files from MP4 to M4A manually or some kind of automated/batch method.
The correct parameters are:
~/foo/bar/bin/ffmpeg -i %input -acodec copy -vn %output
You can set up an Automator process as a Service so you have it under the Contextual menu when you Right-click, or you can set up the download folder for YT Downloader to be the target for a Automated process where the MP4 is converted to an m4a, then added to the iTunes/Music.app directory automatically.