WordPress strips out iframes by default. Which is why you can see it in the editor but not when you try to save/publish this on your site.
Try enabling iframes by adding this to your themes functions.php file
/**
* Add iFrame to allowed wp_kses_post tags
*
* @param string $tags Allowed tags, attributes, and/or entities.
* @param string $context Context to judge allowed tags by. Allowed values are 'post',
*
* @return mixed
*/
add_filter( 'wp_kses_allowed_html', 'allow_iframe_in_editor', 10, 2 );
function allow_iframe_in_editor( $tags, $context ) {
if( 'post' === $context ) {
$tags['iframe'] = array(
'allowfullscreen' => TRUE,
'frameborder' => TRUE,
'height' => TRUE,
'src' => TRUE,
'style' => TRUE,
'width' => TRUE,
);
}
return $tags;
}