I think you have to use get_sub_field
instead of the_sub_field
…
function horairesEte() {
if( have_rows('horaires_ete', 'option') ):
while ( have_rows('horaires_ete', 'option') ) : the_row();
return '<span class="jours">'.get_sub_field('jours').'</span><span class="ouverture">'.get_sub_field('ouverture').'</span>-<span class="fermeture">'.get_sub_field('fermeture').'</span>';
endwhile;
endif;
}
add_shortcode('horaires_ete', 'horairesEte');