RSS Feed invalidate - Podcast artwork must be between 1400 x 1400 and 3000 x 3000 pixels etc

The URL in your 'itunes:image' tag is http://i1.sndcdn.com/avatars-000209134224-riz0yj-original.jpg - this leads to an image which is 879 x 879px and thus far too small to be accepted.

You have a further problem which needs to be addressed. When you enter the URL of your media files in a browser they download instead of playing within the browser as they should. This means that although they work in the iTunes application, the Store may not be able to play them within its own page. This may cause the feed to be rejected.

You need to set each file not to download. eiznem has posted the process:

https://discussions.apple.com/thread/6523821?answerId=26564459022#26564459022

I've re-checked the top episode and it's still forcing a download. If you've got it set not to download I don't know what causes that, though others have complained of the same thing. Once you've got the image sorted out (check it from the URL in the feed in case Soundcloud is reducing the size) try validiating it in Podcasts Connect and see whether any objections are raised. If it tells you it's having difficulty downloading episodes from your feed you'll need to try to find out why this is happening. I'm afraid I can't advise on Soundcloud.

Yes, the image is now 2500 x 2500 which is fine. As the audio files still download it looks as if they are no longer bothered by that - which is a welcome change from a month or two back.