i think the issue may be related to the content of the rss feed perhaps as it contained audio as well. Maybe that is tripping it up.
Discussion
I literally only tested substsck for rss. Thanks for reporting backš«”
Will provide updates
Got a link to your letters? Curious how it looks nostr:npub1xjfd6s75j63r0azyrlvqrag83d34gtp7zk8la2grevpq5xh5llws9lwuey