CF7 auto-wraps elements in spans, add this snippet to functions.php to stop it. Required for MaterializeCSS to operate properly.
add_filter('wpcf7_form_elements', function($content) {
$content = preg_replace('/<(span).*?class="\s*(?:.*\s)?wpcf7-form-control-wrap(?:\s[^"]+)?\s*"[^\>]*>(.*)<\/\1>/i', '\2', $content);
return $content;
});