Even if you find the correct art off the web and manually change it back to what it should be. The system still thinks it is whatever album it incorrectly place as the art. You can verify this by clicking the "show this album in iTunes" (or however it's labeled) and it will take you to the album on iTunes that the incorrect art was.
Another thing it does too (part of the art mislabeling.) say the album has some older songs but they are a totally newer recording/version, it in many cases will "upload" as the older/original version (thus why art gets all jacked up.)
iCloud Music Library is a mess and kinda defeats the whole purpose of having it. When all devices (aside from the locally stored music you uploaded from your Mac.) is not even close to the same and highly inaccurate.