1. logged in as a teacher
2. clicked on an assignment (type not important) -> "view/grade all submissions"
3. clicked on a grading icon in a "Grade" column, for an existing submission
4. Error message:

Notice: Undefined offset: -1 in /html/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()