Music library not found.

No suggestions, I’m afraid, but I have exactly the same problem. I’ve been patiently waiting for a relevant Sonos update for months. I’ve tried to follow the most recent instructions to the letter, and then spent hours trying to see what I’ve done wrong. Earlier today the library appeared, albeit with the “Something Went Wrong” message when I actually wanted to use it. Then it disappeared completely.

My library is on an external hard drive connected to a Windows 10 laptop. It is fine on the laptop app, but not iPad or iPhone.

I spent years constructing the library, it’s hugely disappointing 

There are a number of threads about this. Sonos has dropped (like most of the industry) support for a protocol called SMB1 due to security weakness. The windows app still works with SMB1. Try a search on SMB1 or SMB2 and you will find a couple of threads with detailed info.

My suggestion is to search the forum what whatever your problem is. If you post again, you’re going to have to need to provide some actual information about what your config is and what your problem is.