Return of a similar issue reported and address back in the summer (2023). When searching the “My Music” subdirectory in the Amazon Music Service menu, the display of the artists and albums in the My Music library subdirectory is incomplete. The good news is that the music is there & can be accessed by searching. The problem appears to be solely that you can not look up all of the artists and albums in the subdirectory if you trying to make a selection of music to listen to.
I called this into Sonos support 7-10 days ago. No change as of today (12/5). I appreciate that Sonos may need to engage with Amazon to resolve. Are other users experiencing this again? Please post if you are so we can help move the issue forward to resolution. Thanks all.