Music/ Album artwork not showing on IOS app

The album artwork is not loading for all of my music when viewing on the IOS app, the MyCloud doesnt appear to want to create thumbnails for certain albums.

All my music is tagged using Media Monkey and the art work is saved to the tag.

When uploading music the My Cloud creates two versions of the image and places them in the album folder.

I have tried remote access library rebuild to no avail.
I have tried removing albums and reloading them, sometimes this works but not always.

Does anyone have any tips to ensure the artwork is correctly indexed and thrumbnail created for use in the mobile app?

Hello, What type of images are you using for the album art?

Jpegs embedded using Media Monkey