Malformed URLs appear in the platform in Analytics reports. We display Malformed URLs in the platform when the URL provided by the integrated analytics isn't actually a URL. Oftentimes this is a string of characters that are not in the same format as the other URLs.
Example
An example of this would be (not set) seen in Google Analytics, more information on what that means is available here: https://support.google.com/analytics/answer/2820717?hl=en
The (not set) URL, seen in Google Analytics, would be appended to the protocol and domain name, such as https://www.example.com, and would appear as https://www.example.com/(not%20set) when we retrieve it and thus gets attributed to https://www.examplewebsite.com/MALFORMED-URL.