Thanks for reply.
but it looks doesn’t work. even i hard code the post id.
<?php echo get_field('students_no_class', get_queried_object() , 456 ) ?>
Just did more test.
When I delete author.php
the author page will jump to archive page and coustom field value did not show up.
(in archive.php I can see coustom field value)
here is author page url:
http://domianname.com/?author=123
here is archive page url:
http://domianname.com/?cat=456