Hello --
You won't be able to include Music Library tracks in your bundles unfortunately. Go Button is not allowed to copy tracks out of the on-device Music Library. (No third-party app can, for that matter.)
So if your show has cues that use Music Library tracks and you want to share a bundled show, you'll need to find a way to get those tracks imported as audio files into the Go Button documents folder first. After importing, you don't need to rebuild your show completely, but you will need to edit your cues and hits that use Music tracks and point them to use the imported audio file from your Documents folder instead.
In general terms, the Music Library is convenient and gives you a quick way to access music for your shows that is already on your device. But it does have limitations like you've discovered not being able to include those tracks in bundles, along with sync hiccups which can result in "Missing Media File" problems. For these reasons, we do suggest people try to import their audio files whenever possible, because having your source audio all under Go Button's control is better in the long term.
We talk about importing in a bit more detail in the Go Button documentation here:
Brent