Normally, I'd be right up there with Fox on the "get me a cluebat" train, but I find it interesting that fakecake choked on it as well. I just ran it on the feed checker myself, and had no issues. Tried to diagnose what was going on, and the feed has absolutely no line breaks in it. As far as I know, the client doesn't act as a middleman and fakecake does the fetching itself, so I have zero idea what happened there.
But in the interests of thoroughness, pulled down latest release (63f0ed3), added feed... confirmed that the images that loaded perfectly fine were .jpg, since some were .png. Problem not reproduced. I'm not going to verify that the .jpg files really are JPG. Going to guess there's a config or referrer issue here, unless someone can prove that TTRSS (and not the feed) is producing an invalid image URL.
I'm genuinely curious why the feed checker had different outputs, but even then, a LibXML error means someone can't be bothered to follow XML specifications, which isn't a TT-RSS problem. You know, that thing that answers 99% of "my feed doesn't work" threads, even after a sticky was made to try and get people to stop asking about it.