Clicking the "submitted assignments" link, to view the list of students for grading, i get:

See all course grades
Warning: mysqli::query(): (22003/1690): BIGINT UNSIGNED value is out of range in '(`moodle`.`s`.`timemarked` - `moodle`.`s`.`timemodified`)' in /var/www/html/moodle/lib/dml/mysqli_native_moodle_database.php on line 793

Error reading from database

More information about this error
Debug info: BIGINT UNSIGNED value is out of range in '(`moodle`.`s`.`timemarked` - `moodle`.`s`.`timemodified`)'
SELECT u.id,u.picture,u.firstname,u.lastname,u.imagealt,u.email,
s.id AS submissionid, s.grade, s.submissioncomment,
s.timemodified, s.timemarked,
COALESCE(SIGN(SIGN(s.timemarked) + SIGN(s.timemarked - s.timemodified)), 0) AS status FROM mdl_user u LEFT JOIN mdl_assignment_submissions s ON u.id = s.userid
AND s.assignment = 8 WHERE u.id IN (11,68,107,111,45,90,43,91,71,4) ORDER BY lastname ASC
[array (
)]
Stack trace:

line 391 of /lib/dml/moodle_database.php: dml_read_exception thrown
line 794 of /lib/dml/mysqli_native_moodle_database.php: call to moodle_database->query_end()
line 1295 of /mod/assignment/lib.php: call to mysqli_native_moodle_database->get_records_sql()
line 642 of /mod/assignment/lib.php: call to assignment_base->display_submissions()
line 369 of /mod/assignment/type/upload/assignment.class.php: call to assignment_base->submissions()
line 57 of /mod/assignment/submissions.php: call to assignment_upload->submissions()