Album Art not working at all

I have just swapped from Rune Audio to Volumio and it’s certainly a lot better in all areas apart from album art. I’ve read many posts on the forum and tried quite a few of the suggestions with no success. The setup is an Pi 2 with Volumio 2.513 installed on a 8G card. All media is streamed from a NAS setup with a CIFS share. All of my NAS music is stored in album folders under an artist top level folder. Each album has Folder.jpg album artwork and each MP3 has the same image embedded. I get no album art at all. The music folder is fairly large so I have tried a single album folder setup and pointed Volumio at that alone - still no artwork. I’ve changed the artwork name from Folder.jpg to folder.jpg - no effect. Tried a 32G card as a test - no effect.
So I think i’m stumped - has anyone got any ideas as to what is going on.
For reference I use Madsonic music server on the same data source for mobile music and get all of the album art so it’s not a format issue.
I’d be keen to see if anyone else has similar problems or am I missing something?

To understand: are you browsing via Media Servers?
If that’s the case, can you point us to the media server that you use?

All of the media is stored on a NAS on my internal network. The NAS isn’t accessible from the internet for security reasons unfortunately. It’s all local with all boxes on the same subnet and streaming from the NAS works without any problems so I’ve ruled out a network setup issue.
I have just re-scanned the entire media set and oddly I do get the very occasional album art displayed. I’ve so far spotted two in about 100-150 folders so a very low number. I’ve looked at those folders and can’t see any difference in image name or format to those that aren’t displayed. There is one that was a .jpeg rather than .jpg but a quick test with a non-displayed artwork showed that the extension didn’t make any difference (after a Reset Album Art Cache)

how big are those images?

In general the images range from about 5Kb to 150Kb. Specifically, the ones that were displayed are 9Kb, 75kb and 114Kb so quite a range.

An interesting observation - The album art is not showing up through the ‘Music Library’ but works perfectly when browsed through ‘Media Servers’ so this must point at a parsing or database issue in the Music Library area.