Same for me…

This happens since ACF Version 5.6.6 because ACF changed the DOM and the <p class="acfw-no-acf"> is no longer a sibling of the "div[id*='_acf_widget_'] .acf-field" as it would be searched in the acf-widgets.js

If you change the acf-widgets.js to this, it works on ACF 5.6.6 and newer as well:

function acfw(){
  var el = jQuery("div[id*='_acf_widget_'] .acf-field");
  var num = 0;
  num = el.length;
  if ( num > 0 ){
    var remove = el.closest('.widget-content').children('.acfw-no-acf');
    remove.attr('data-display', 'none');
  }
}
function acfw_remove_fields(){ 
  jQuery('.widget .acf-field').remove(); 
}
jQuery(document).ready( acfw );