In some cases, creating an assignment with 'remind me to grade by' unchecked fails with the following error:

Debug info: Deadlock found when trying to get lock; try restarting transaction
DELETE FROM mdl_event WHERE modulename = ? AND instance = ? AND eventtype = ?
[array (
0 => 'assign',
1 => '53500',
2 => 'gradingdue',
)]
Error code: dmlwriteexception
Stack trace:
line 489 of /lib/dml/moodle_database.php: dml_write_exception thrown
line 1625 of /lib/dml/mysqli_native_moodle_database.php: call to moodle_database->query_end()
line 1911 of /lib/dml/moodle_database.php: call to mysqli_native_moodle_database->delete_records_select()
line 1227 of /mod/assign/locallib.php: call to moodle_database->delete_records()
line 702 of /mod/assign/locallib.php: call to assign->update_calendar()
line 41 of /mod/assign/lib.php: call to assign->add_instance()
line 124 of /course/modlib.php: call to assign_add_instance()
line 154 of /course/modedit.php: call to add_moduleinfo()

We're currently running 3.7.1+, but have seen this issue since about 3.3.x. It's intermittent, occuring during busy times.

Related bugs -
https://tracker.moodle.org/browse/CONTRIB-7241
https://tracker.moodle.org/browse/MDL-63732