After many times replacing the various .plist, .tl files and .xml files from the time machine backup I keep ending up with the last available. Playlist library containing a “test” playlist.
I found the .plist that was holding the “test” playlist in the ~/Library. Unfortunately
there is no similar .plist available in the Time Machine history.
My conclusion is that something must have changed that is beyond our control and I cannot recover from a backup.
iMazing saved the day.
I was able to restore the playlist from the iPhone back to Music.
The process was a little bit messy but nothing I could not fix by deleting duplicate playlist. Easy enough, much better then hand crafting 15 playlist with each up to 100 tracks…