After upgrading Moodle to 2.3.3 the links in the gradebook table no longer lead to the correct student. Rownum for the first student is "-1". Clicking this leads to a "programming error" page.

e.g.
view.php?id=9844&rownum=-1&action=grade

mod/assign/gradingtable.php

I changed line in class assign_grading_table extends table_sql implements renderable {
private $rownum = -1;

to
private $rownum = 0;

And the grading table is now linking to the correct student. I don't know if this is a suitable fix but is working for now.