Contacted apple, they say that they're now aware of an issue and engineering are working on a fix... so that's good! Hopefully sooner rather than later
I hope they fix it very soon. For the time being I've turned off the stupid iCloud Music Library, which sucks, but I really can't stand how (tried 4 times re-syncing) it changes so much album art (either does some other random album from the same artist or a totally different artist all together.)
Why must it even touch what I have locally on my phone that has been synced from my iMac? So stupid. I've tried both Merge and Replace options when turning on the iCloud Music Library, same result every single time. I spent many, many hours while on 8.4 beta getting all correct and high res album art for everything and Apple Music just ruins and throws all that away.
It actually even deletes a couple of my albums completely when turning on iCloud Music Library. I would love an option when turning on the Library that does not touch what I have ON my phone already, so that I could actually use Apple Music fully.