iPhone showing odd default album art

Hi, for a few years now I've had an issue where my iPhone shows the cover art from a podcast instead of the default "no art" art on music items without artwork. It looks correct on my computer, but on the iPhone it's as if the default artwork has been replaced. I have tried several different fixes, including:

• Completely deleting and restoring my music library
• Deleting my iPhone connection from my computer and re-syncing from scratch
• Deleting and restoring the Music app from my phone
• Disconnecting and reconnecting my iCloud account from my phone

but yet I'm still getting the wrong default artwork for albums without artwork.

For albums which do get artwork it displays correctly, but not all of the music in my library has artwork available (and my collection goes back decades, much of it being obscure stuff that's otherwise lost to time or has never been on the iTunes Music Store).

The specific artwork that appears is for the NPR podcast "Invisibilia," and that's been the case for years. It's such a strange mystery. That podcast isn't even downloaded to my phone!

Are there any other methods for resetting the default album art that I've possibly missed?