So your music tags got totally fucked up in your Android player.
In my case, each and every song got album art from 2 Unlimited album. Probably just because the name 2 Unlimited starts with a digit, which makes it the first file in my file list. To try and solve this problem, go into the settings of the app you use for playback, in my case it’s Rocket player. Delete all the app data. The next thing to find is the tracker You may notice that Linuxoids are not really tidy and like most nerds, live in complete mess of a room. The mess in the heads translates into the software they create. If you ever tried to find out the folders an Ubuntu app installs itself into, you know what I mean. Instead of having one folder for music, they developed a meta tracker utility, which tracks all the media files on the drive and creates an index of them. So you may continue to save the files at random locations, and still be able to find them in this index. Android music player relies on this index, and this index got fucked up in my case. So find Media Storage app and wipe its settings. Then reboot the phone and leave it be for half an hour. The tracker should finish building a new media files index by then, and this fixed my album art problem. I also recommend AIMP player, which recently became available for Android. It completely ditches the Android system tracker and builds it’s own index with blackjack and hookers.