I’ve been notified of a crash that can occur when having TypeMetal connect to a WordPress site on macOS 10.13.3. It appears to be the inadvertent result of a relatively recent change in WebKit.
When configuring TypeMetal to connect to your WordPress blog, make sure to explicitly specify a custom XML-RPC URL that begins with “https:” if your site is configured to support secure transport (https), as described on this page of the user guide under “Custom XML-RPC URLs”. (If you see a padlock icon in Safari’s title bar when visiting your site in Safari, then your site is set up to use secure transport.) At least one user has found that this prevents the crash and enables TypeMetal to connect successfully.