Hello,
you have some cloudfare anti bot check on the RSS sites. ....
here the some of the output with curl:
$ curl https://www.scribblehub.com/rssfeed.php?type=series&sid=93826
[1] 163371
$ <!DOCTYPE HTML>
<html lang="en-US">
<head>
<meta charset="UTF-8" />
<meta http-equiv="Content-Type"...