This actually happened to us at moodle.org. Notification email was sent to user with privacy officer role on moodle.org:

Exception occured while processing privacy data

Exception occured while calling editor_atto\privacy\provider::get_contexts_for_userid.
This means that plugin editor_atto did not complete processing data. Below you can find exception information that can be passed to the plugin developer.

Invalid user

#0 /var/www/vhosts/moodle.org/html/lib/dml/moodle_database.php(1522): moodle_database->get_record_select('user', 'WHERE id = ? AN...', Array, 'id', 2)
#1 /var/www/vhosts/moodle.org/html/lib/accesslib.php(6115): moodle_database->get_record('user', Array, 'id', 2)
#2 /var/www/vhosts/moodle.org/html/lib/editor/atto/classes/privacy/provider.php(75): context_user::instance(2438070)
#3 /var/www/vhosts/moodle.org/html/lib/moodlelib.php(7764): editor_atto\privacy\provider::get_contexts_for_userid(2438070)
#4 /var/www/vhosts/moodle.org/html/privacy/classes/manager.php(495): component_class_callback('editor_atto
pri...', 'get_contexts_fo...', Array)
#5 /var/www/vhosts/moodle.org/html/privacy/classes/manager.php(528): core_privacy\manager::component_class_callback('editor_atto', 'core_privacy
lo...', 'get_contexts_fo...', Array)
#6 /var/www/vhosts/moodle.org/html/privacy/classes/manager.php(237): core_privacy\manager->handled_component_class_callback('editor_atto', 'core_privacy
lo...', 'get_contexts_fo...', Array)
#7 /var/www/vhosts/moodle.org/html/admin/tool/dataprivacy/classes/task/initiate_data_request_task.php(102): core_privacy\manager->get_contexts_for_userid(2438070)
#8 /var/www/vhosts/moodle.org/html/lib/cronlib.php(185): tool_dataprivacy\task\initiate_data_request_task->execute()
#9 /var/www/vhosts/moodle.org/html/lib/cronlib.php(74): cron_run_inner_adhoc_task(Object(tool_dataprivacy\task\initiate_data_request_task))
#10 /var/www/vhosts/moodle.org/html/admin/cli/cron.php(61): cron_run()
#11 {main}

Edited by mudrd8mz - corrected the line number in the stack and clarified the title.