Thanks- feedvalidator was a great help.
Part of the issue is that instead of
[(site_url)][~[+id+]~]
in my RSS chunk, I had changed it to pass along a URL that is external to my site that is associated with a document object. Sometimes, those have unfriendly URLs with ’?’ in them, which RSS validator doesn’t like.
I then changed it back to my own id and, voila’ everything works fine. Still, in order to achieve the experience I want, I made a snippet [[redirect]] to give those id’s a 301 redirect to that same external URL.
my template calls it with
[!redirect? &newslink=`[*newslink*]`!]
but of course, any URL with a ’?’ in it sends the user to a dead end. So, I just need to figure out my snippet call, i think...