It appears the post meta is not being cleared for ‘sunday’ when the checkbox is unchecked.
If( isset($_POST['sunday']) ){
update_post_meta($post->ID, "sunday", $_POST["sunday"] );
}else{
delete_post_meta($post->ID, "sunday");
}
return $post;
Or you can set the value to false
If( isset($_POST['sunday']) ){
update_post_meta($post->ID, "sunday", true );
}else{
update_post_meta($post->ID, "sunday", false );
}
return $post;