iTunes 12.2: This is really a bit of a drag. I need help from the crowd.

Among the things that have happened - and clearly not just to me - since I "upgraded" to iTunes 12.2.0.145:

On my laptop, nearly 15,000 songs disappeared;

On my desktop and laptop, media files were changed, and metadata was overwritten by other metadata, making it look like I had duplicate songs;

On my desktop and laptop, I can no longer look pull up the library from one machine onto another (which I used to use for comparison, and to make sure both libraries were in sync);

I've re-installed the library from a Time Machine backup, but still songs are missing.

I've moved and re-created the itl and xml files.

I've organized, re-organized, shared and unshared and clicked everything I could possibly, but still nothing.

I've got a call in to Level 2 tech support, but from what I gather, what's happening is a mystery.

Any thoughts from the madding crowd?