I THINK I GOT IT!
In the Php file of the gallery there was a limit of 100 posts for page. I changed it to 500. It seems like they reappeared.
thanks ! you helped!
<?php $argsau = array( ‘post_type’ => ‘gallery’, ‘order’ => ‘DESC’,’orderby’ => ‘date’,’posts_per_page’ => ‘500’ );
$loopau = new WP_Query( $argsau );
while ( $loopau->have_posts() ) : $loopau->the_post();
$termscat= get_the_terms( $post->ID, ‘gallery_category’);
$thumb =wp_get_attachment_image_src( get_post_thumbnail_id(get_the_ID()), ‘thumbnails-pot’ );;
$url = $thumb[‘0’];
?>