I happen to think its nice.

Its just a learning curve, like any new software, you learn your way around it..

If you had your music on a NAS, PC or Mac, try enabling SMB v2 or 3 since SMB v1 is no longer supported.

I like the new app. While some have issues, it has worked well for me from day 1. I'm excited to see the full functionality of it when everything works. I hope they allow you to customize favorite screens to have quicker access to the screens you use most.

You may be in the minority.   Why has some of my music and playlists disappeared?  

I'm not clear on what you mean. Are you asking about streaming services or a local library?

Sonos playlists.