When a student submits a file assignment they receive the following. Activity completion is enabled with a minimum grade (not sure if this is relevant).

Invalid user

More information about this error

Debug info: SELECT id FROM

Unknown macro: {user}

WHERE id = ? AND deleted = ?
[array (
0 => -10,
1 => 0,
)]
Error code: invaliduser
Stack trace:
line 1451 of /lib/dml/moodle_database.php: dml_missing_record_exception thrown
line 1427 of /lib/dml/moodle_database.php: call to moodle_database->get_record_select()
line 6390 of /lib/accesslib.php: call to moodle_database->get_record()
line 253 of /lib/messagelib.php: call to context_user::instance()
line 4547 of /mod/assign/locallib.php: call to message_send()
line 4576 of /mod/assign/locallib.php: call to assign::send_assignment_notification()
line 4629 of /mod/assign/locallib.php: call to assign->send_notification()
line 5564 of /mod/assign/locallib.php: call to assign->notify_student_submission_receipt()
line 5610 of /mod/assign/locallib.php: call to assign->save_submission()
line 387 of /mod/assign/locallib.php: call to assign->process_save_submission()
line 53 of /mod/assign/view.php: call to assign->view()
Output buffer: <div class="notifytiny debuggingmessage" data-rel="debugging">Warning: logged very long URL<ul style="text-align: left" data-rel="backtrace"><li>line 177 of /admin/tool/log/store/legacy/classes/log/store.php: call to debugging()</li><li>line 165 of /admin/tool/log/classes/log/manager.php: call to logstore_legacy\log\store->legacy_add_to_log()</li><li>line ? of unknownfile: call to tool_log\log\manager->legacy_add_to_log()</li><li>line 595 of /lib/classes/event/base.php: call to call_user_func_array()</li><li>line 5889 of /lib/moodlelib.php: call to core\event\base->trigger()</li><li>line 88 of /message/output/email/message_output_email.php: call to email_to_user()</li><li>line 230 of /lib/messagelib.php: call to message_output_email->send_message()</li><li>line 4547 of /mod/assign/locallib.php: call to message_send()</li><li>line 4576 of /mod/assign/locallib.php: call to assign::send_assignment_notification()</li><li>line 4629 of /mod/assign/locallib.php: call to assign->send_notification()</li><li>line 5564 of /mod/assign/locallib.php: call to assign->notify_student_submission_receipt()</li><li>line 5610 of /mod/assign/locallib.php: call to assign->save_submission()</li><li>line 387 of /mod/assign/locallib.php: call to assign->process_save_submission()</li><li>line 53 of /mod/assign/view.php: call to assign->view()</li></ul></div><div class="notifytiny debuggingmessage" data-rel="debugging">Error calling message processor email<ul style="text-align: left" data-rel="backtrace"><li>line 231 of /lib/messagelib.php: call to debugging()</li><li>line 4547 of /mod/assign/locallib.php: call to message_send()</li><li>line 4576 of /mod/assign/locallib.php: call to assign::send_assignment_notification()</li><li>line 4629 of /mod/assign/locallib.php: call to assign->send_notification()</li><li>line 5564 of /mod/assign/locallib.php: call to assign->notify_student_submission_receipt()</li><li>line 5610 of /mod/assign/locallib.php: call to assign->save_submission()</li><li>line 387 of /mod/assign/locallib.php: call to assign->process_save_submission()</li><li>line 53 of /mod/assign/view.php: call to assign->view()</li></ul></div>