If you’re still struggling with this error, I figured out what caused mine…
After searching the codex I learned that the “home_url” variable is called by ../wp-includes/link-template.php. This variable is populated by whatever the user puts in Dashboard -> Settings -> General -> “Site Address (URL)”.
When I looked at mine I had a fully-formed URL in my “WordPress Address (URL)” field (https://frydaho.com), but only “frydaho.com” in the “Site Address (URL)”. I tossed “https://” in front of it and, voila!, no more malformed URL complaint from Jetpack!
Here is a screenshot…
