Hi, I think I found the solution (not sure 100% because I’m not a programmer).
I saw that in functions.php there is the “add_theme_support” for “post_thumbnails” but just for post, portfolio and gallery format. This is the script [LINE 244, functions.php]:
If I add to functions.php (in my child theme) a simple support with no array, the post_thumbnails area appears also in custom post editor. This is the line of code I added and now everything works fine:
if (function_exists(‘add_theme_support’)) {
add_theme_support(‘post-thumbnails’);
}