If I go into an instance of mod_assign where a student has a graded submission and click on the tick icon in the grade column I get the following. The URL is /mod/assign/view.php?id=104&rownum=-1&action=grade

Notice: Undefined offset: -1 in /home/andrew/Desktop/code/moodle/dev/master/mod/assign/locallib.php on line 2068

Coding error detected, it must be fixed by a programmer: Row is out of bounds for the current grading table: -1

More information about this error
Debug info:
Error code: codingerror
Stack trace:

line 2073 of /mod/assign/locallib.php: coding_exception thrown
line 398 of /mod/assign/locallib.php: call to assign->view_single_grade_page()
line 53 of /mod/assign/view.php: call to assign->view()