The User Session query returns inaccurate result as it does not include WebDesk session?
The User Session query is available as a system query and give the possibility to list of session running on Service Desk (i.e.: console, WebDesk, Service Portal)
The User Session query criteria is set with a criteria Client Type is one of 1,2 and you would need to include 0.
0 as a client type refer to WebDesk client session
1 as a client type refer to Console client session
2 as a client type refer to Service Portal client session
You may also add a criteria to exclude SA user session to filter the query.
To do so add a criteria on User.Title attribute "Is not Equal To" SA