RSS feed issues – functions.php file

Hello, Recently the RSS feed is showing invalid parsing errors: https://validator.w3.org/feed/check.cgi?url=https%3A%2F%2Ffeeds.feedburner.com%2Fpmags line 8, column 44: XML parsing error: <unknown>:8:44: not well-formed (invalid token) This issues only came about in the past week or so. From what I found via searches, a potential culprit is the functions.php file found in the theme directory folder. I have not modified that file in quite some time. I upgraded my Catchbox Pro theme as a possible solution just now. Still broken. Any thoughts? thank you, Paul