I have found that connecting MusicBee with BubbleUPnP seems to always give me blurry album artworks. I have set my image quality to be 100, in the MusicBee UPnP plugin I have the image as 3000px and even forced bubbleUPnP to rescan my files but it always seems to come out blurry for some reason.
In MusicBee my images are embedded within the music file so it should be pulling through with full quality.
Not sure what is going on there.