Limitations and Restrictions
If other users are connected to the database at the time that you set the database to single-user mode, their connections to the database will be closed without warning.
The database remains in single-user mode even if the user that set the option logs off. At that point, a different user, but only one, can connect to the database.
Before you set the database to SINGLE_USER, verify that the AUTO_UPDATE_STATISTICS_ASYNC option is set to OFF. When this option is set to ON, the background thread that is used to update statistics takes a connection against the database, and you will be unable to access the database in single-user mode.