How to display ACF coustom field from category on author.php

In ACF for Authors, you need to supply the author in 'user_'.$user_id format.

Which would be this:

echo get_field( 'students_no_class', 'user_'. get_queried_object()->ID );

or this:

the_field( 'students_no_class', 'user_'. get_queried_object()->ID );