Thanks for reaching out!
The thing is, that there is no exact way to embed an Artist artwork to your music files. All software that displays an Artist artwork uses external sources (music files you have imported - never contain the Artist artwork, only the Album artwork).
VOX is using public sources to import Artist artworks and display them, unfortunately, some of the resources have been closed or blocked unexpectedly, that is why we need to look for new, alternative sources to use them to populate the Artists with proper artworks.
Additionally, we are looking forward to introducing new features, that will provide our users with the ability to import their own Artist artworks or Album artworks!
This should be fixed in the next version of VOX app. Thanks!
(also Feedback text box in which I’m writing this is black on very dark grey, so I can’t really see what I’m writing).