While I wait for Apple to fix their bugs  I figured I’d try a refresh of my iTunes Library. It’s unlikely to hurt, and I have abundant backups. 
It’s a very old trick — so old I’d all but forgotten it. You just move your iTunes Media folder (advanced prefs, organize, etc). I’ve done this a few times over the past 10-12 years and it’s generally worked well. It’s really a copy, not a move, so if everything is fine you can delete your old files . You need a lot of disk space of course, but external drives are cheap these days.
During the move it’s a good idea to turn off backup, especially Time Machine. Otherwise you’ll run into drive churn slowdowns. Just be sure to create a reminder to turn backup on again the next morning. (On my system this takes hours to complete, so I run it overnight.)
I figure if there are any file or database corruption problems this might clear them up. At least it ensures that everything has been touched by the current (icky) version of iTunes and all files have been freshly written to disk.
- fn -
 Given all of Apple’s recent software quality problems, I sometimes wonder about industrial sabotage.
 I’m at the point where I’m looking for hardware issues. One trick is to switch to WiFi sync — eliminates issues with USB cables, USB hub, USB ports, etc.
 I like to rename the original folder and let it sit for a few weeks. I create a reminder to delete it then.
The library move seemed to go as smoothly as ever. Subsequent syncs were quick and trouble free, but only time will tell if anything has truly improved.