Yes, there seems to be a problem.
Used to work 2 weeks ago, when i last tagged an Album.
Need to debug the issue.
Hope to find some time tomorrow.
Amazon approved my request, so i was able to change the call to the API.
Version 3.0.3, which i just have released, can retrieve cover art again.
Just post a sample search string, i.e. an Artist / album, to search for, and i'll try reproducing it.