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