album artwork showing up intermittently

Here are some artwork details.

 Do you have tagging software like MP3 Tag?  Tagging software will show you if the music file has an album cover as part of the metadata.  Some systems look for a jpg/png album cover file in the album folder containing the music track files.  Some systems look for the album cover in the tag metadata.

I use Bliss - it might tell me. I’m pretty sure the albums in question are tagged internally, which I think is what Sonos actually uses. The stuff shows up fine in finder, apple music, etc…

 Does an album in Sonos with missing album art show the album art in Bliss?  In my library I have a jpg/png album cover file in all my albums.  Also all albums are tagged with the album art as part of the metadata.  The only pain-in-the-butt system is Bryston who uses MPD requiring me to name all the jpg/png files with the same name.  In the MPD settings I set the name to “cover.jpg”.

Yes, everything looks great in Bliss. and (due to mistakes) I had bliss generate cover.jpg/png and folder.jpg/png

I could, at least potentially, see a wifi interference issue, for the moment the controller is requesting the album art…but I’d think it would be random, not easily repeatable. Nor do I have any knowledge about sequences in data requests through the Sonos controller. But I’d definitely expect it to be random. 
 

I do think the controller doesn’t ask for the art directly, I expect the Sonos devices to request it, and ‘publish’ it to the controller, as they do with everything else they process. It would be odd for a controller to be responsible for such a minor thing, when the Sonos device itself is responsible for everything else. 

Bliss has pretty decent tag editing, but which tag has art in it?

I kind out doubt that it’s interference. for affected albums I can never, ever get the art. And I do have some wired devices. Also. for a long time I had no issues - now all of a sudden (with a lot of new equipment) I have this problem.

Here is what it looks like in apple music (presumably using embedded art?):
 

Here is what it looks like in Bliss, on my Mac:

 

And after everything copied to NAS, finder at least shows the folder and cover png:
 

I just downloaded mp3 tag, but how do I use it to see embedded art? Here’s a file that shows correctly, but I don’t see where it says anything about art?