If I have my iPhone connected to my car over USB the album art and track length are incorrect. If I play any song, and let it complete the song and go to the next song in the playlist, the album art and track length will be for the previous song, and stay one song behind for the whole playlist. So if the previous song was for 3 minutes, and the current song is 7 minutes long, the car will show a song length of 3 minutes. However, if I skip to the next song without letting it play through, the album art and track length displayed on the car will be corrected and shown accurately for the current track.
I did this on the way to work one day, and when I got back in the car at the end of the day the Spotify app resumed playing over USB but the track length and album art was still showing for the previous song, so it's definitely sending the wrong info, and not caused by the car. The track length and album art shown on my phone screen are correct but different to what's being shown on the car.
(this seems to me like a list index issue where the index for sending the track length and album art are out by 1, compared to the track title data, for the current track in a playlist).
This is easily able to be replicated. I can send you a photo if you need it.