Podcast art not updating on iPhones

So I recently (more than 2 weeks ago) changed my podcast's art. The new art is 3000x3000 px and shows up in the desktop app properly.

However, in my Apple iPhone podcast app, I see the old art. Other listeners have contacted me saying they see no art or the old art. How can I force my phone app to update the art settings? Seems like they're cached and not being triggered to update despite the new art having a different file name?

Is there any way to trigger an art update or clear art cache from the Podcasts app?

My show's feed on iTunes is here.