While "proxy-url-file-3A-2F-2F-2F" looks like a technical error or a specific file path, it is actually a version of a common string used in proxy configurations and web development.
did you find this string? (e.g., in a browser address bar , a system log , or an email ?) Is it associated with a specific program ? proxy-url-file-3A-2F-2F-2F
So %3A%2F%2F%2F decodes to :/// .