All podcasts hosted on megaphone.fm are failing with HTTP error 400. They seem to work with other podcast apps, but not with DoggCatcher. It doesn't matter which podcast you try, they all fail, but as an example you can try Rooster Teeth Podcast if you want to try to replicate the error. Podcasts hosted on other hosts are working normally. This issue began sometime earlier today, November 25, 2020. Prior to that, they downloaded normally as well.
Update: I was able to "fix" this issue by deleting all of my (long existing) feeds that use megaphone.fm and re-adding them from the Subscribe window. As far as I can tell, all the URLs to the actual RSS feeds are exactly the same, but I no longer get HTTP 400 errors when trying to download from them. Still no idea why the errors came up suddenly in the first place, or how to replicate them 100%, but all seems well now.
Maybe there was an issue with their server