fix feed burner cover art. Search for pbs newshour for examples. or try this link http://feeds.pbs.org/pbs/newshour/headlines-audio
Other podcathers finds art work in feedburber RSS. Podcast addict doesn't.
Please open a ticket using the website Contact support to report an issue. This section is for new feature suggestion. Please avoid adding URL in the ticket subject.
FYI I tried your link and the image isn’t displayed on my web browser. The link is broken so it’s normal that it failed to be displayed in the app. In other app they may have cached an old version of the image