Not sending Email Notifications: `"Backends provided no user object"`

Not sending Email Notifications to users.
Please, help me!
Log shows it:

{"reqId":"H16EbjgcSJA5DtTAXPyy","level":3,"time":"2022-02-28T09:00:02+03:00","remoteAddr":"","user":"--","app":"activity","method":"","url":"--","message":"Failed sending activity email to user \"D9070CCE-7EA9-4E4B-89E3-2E4C1B5EC7EF\"","userAgent":"--","version":"23.0.2.1","exception":{"Exception":"OC\\User\\NoUserException","Message":"Backends provided no user object","Code":0,"Trace":[{"function":"getUserFolder","class":"OC\\Files\\Node\\Root","type":"->"},{"file":"/var/www/nextcloud/lib/private/Files/Node/LazyFolder.php","line":65,"function":"call_user_func_array"},{"file":"/var/www/nextcloud/lib/private/Files/Node/LazyRoot.php","line":40,"function":"__call","class":"OC\\Files\\Node\\LazyFolder","type":"->"},{"file":"/var/www/nextcloud/apps/approval/lib/Activity/ApprovalProvider.php","line":125,"function":"getUserFolder","class":"OC\\Files\\Node\\LazyRoot","type":"->"},{"file":"/var/www/nextcloud/apps/activity/lib/MailQueueHandler.php","line":454,"function":"parse","class":"OCA\\Approval\\Activity\\ApprovalProvider","type":"->"},{"file":"/var/www/nextcloud/apps/activity/lib/MailQueueHandler.php","line":359,"function":"parseEvent","class":"OCA\\Activity\\MailQueueHandler","type":"->"},{"file":"/var/www/nextcloud/apps/activity/lib/MailQueueHandler.php","line":164,"function":"sendEmailToUser","class":"OCA\\Activity\\MailQueueHandler","type":"->"},{"file":"/var/www/nextcloud/apps/activity/lib/BackgroundJob/EmailNotification.php","line":61,"function":"sendEmails","class":"OCA\\Activity\\MailQueueHandler","type":"->"},{"file":"/var/www/nextcloud/lib/private/BackgroundJob/Job.php","line":51,"function":"run","class":"OCA\\Activity\\BackgroundJob\\EmailNotification","type":"->"},{"file":"/var/www/nextcloud/lib/private/BackgroundJob/TimedJob.php","line":58,"function":"execute","class":"OC\\BackgroundJob\\Job","type":"->"},{"file":"/var/www/nextcloud/cron.php","line":128,"function":"execute","class":"OC\\BackgroundJob\\TimedJob","type":"->"}],"File":"/var/www/nextcloud/lib/private/Files/Node/Root.php","Line":372,"CustomMessage":"Failed sending activity email to user \"D9070CCE-7EA9-4E4B-89E3-2E4C1B5EC7EF\""},"id":"621c64f70a8c6"}

Start with apps/approval/lib/Activity/ApprovalProvider.php at line 125, then trace how apps/activity/lib/MailQueueHandler.php handles the parsed event during cron email processing. Reproduce the notification failure and determine what must change so the activity email completes without the reported NoUserException.