I found that when the album art embedded in an mp3 or flac file is too large (for example 1080x1080), then the SONOS S2 app crashes when trying to load and display it. I tried reducing the album art (to 200x200) and it solved the problem. This issue affects the S2 app on both Windows 10 and Windows 7.
This may explain some of the app crashes reported by S2 users.