Portfolio Revisions not working

I’m using Enfold v2.6.2, and according to this post:
https://kriesi.at/support/topic/revisions-do-not-work/
…it seems that revisions for portfolio items are disabled by default, but there’s a code to enable them.

I have placed this code in a functions.php file in my child theme:

<?php

add_filter('avf_portfolio_cpt_args','avia_add_portfolio_revision', 10, 1);
function avia_add_portfolio_revision($args)
{
  $args['supports'] = array('title','thumbnail','excerpt','editor','comments','revisions');
  return $args;
}

?>

…but the checkbox for revisions is still not showing in the portfolio page screen options.

Is there a way to make them work. Please can you help ASAP?…Things keep breaking on the portfolio page when I’m adding content to tabs, and there’s no way to go back to previous versions. I’m losing hours of work.