Please note that the following steps will erase all your data that is associated with the stuck app (such as documents, preferences, settings, other cached data).You will need to back up your documents before you uninstall the app.
If you have a lot of music and that download happens over a cellular data connection, it could get expensive.
I use a test library for Apple Music, on my Mac Book, that links to my i Pad and i Pod touch.
How difficult it would be to fix, I don't know, but Apple has to decide it is worth their while to look into it before we can find out.
I am hoping that forum members might consider taking a moment to go to Apple's feedback page and send a bug report about this issue.
I could get sighted help to redownload the Enhanced books that are split after figuring out which books will be affected by this problem and then re-edit the metadata yet again for these books, but I really wish Apple would just fix this problem.