Apple Music Album Art (Manually Edited) Not Synching

I am trying to synch my music library from Windows to my iphone. For the albums that Itrunes could find the cover art automatically, it works fine. For those albums to which I had to add the album art manually on the PC, that image does not synch. Is this the way it just is - or is there something I can do? I have tried deleting the library/app on the phone and reinstalling, and it doesn't change this. (It did however fix another issue where it was assigning a cover picture from a pod cast as the album art for all of those unknown album art entries; I deleted that pod cast and resynched and now it just shows no artwork instead of the random one).