NOTE: Prepend table prefix to tables in SQL queries listed below if needed.
- login to Admin Console in 2 different browsers (actions below needs to be taken in one of the browsers only)
 - go to Configuration → Website → Scheduled Tasks section
 - ensure, that only delete_expired_sessions scheduled task is enabled
 - go to Tools → Query Database section
 - execute following SQL: UPDATE UserSessions SET LastAccessed = 0;
 - remember record count in the UserSessions table
 - switch to command line mode
 - execute php tools/cron.php command in In-Portal folder
 - confirm, that there is now only 1 session in UserSessions table