It appears that the recent Sonos update, 13.1, is broken with regards to non-ASCII characters in files when updating the library. I have a job that daily generate 30 playlists, and the format of the name of the playlists is Pnn Artist - Albuim.m3u. They are located on a NAS from Synology that I have had for quite a few years.
For instance, there is a file of which the name is P05 - Järngustav - Tiden läker inga sår.m3u. But in the Windows controller, this appears as P05 - Jrngustav - Tiden lker inga sr.m3u. In the Windows controller I see a square with a cross in instead of the å and the ä. Another example is P23 Cicala Mvta - Live at 磔磔- 結成20周年記念.m3u. Here all Kanji characters comes out as question marks. And it is not only matter of prettiness; when I open the list, there is nothing there, and I can’t put it into the queue.
This was working without problem until yesterday, until it was broken. It obviously needs to be fixed - and fixed soon!