I know this is an old question but maybe we can make some progress – I was able to add the WYSIWYG fields to the Yoast analysis by using this https://github.com/Yoast/YoastSEO.js/blob/develop/docs/Customization.md#example-implementation
– basically you can parse the ACF editor fields and add them to what Yoast is analysing, I’ve added this in the example implementation from above and it seems to be working for now
ExamplePlugin.prototype.myContentModification = function(data) {
var new_content = ”;
jQuery(‘iframe[id^=”acf-editor-“]’).each(function(e){
new_content += ‘ ‘ + jQuery(this).contents().find(‘body’).html();
});
return data + new_content;
};