I can confirm I am having the exact same issue. Every time I import a field group that uses clone fields the clone fields aren’t present screen when editing that field group but are still visible within my acf-json files and on the page they were meant for. Any editing done to that field group removes them however.
I’m not sure what $pf_studi
is in reference to but in scheda.php your PHP should look like
if( get_field('studi') ){
echo '<div class="one_third">';
echo '<h4>Studi</h4>';
echo '<div class="description">';
echo get_field('studi');
echo '</div>';
echo '</div>';
}