This setting is for users being inactive but the timeout is not getting triggered. As a result, user session remained up and running.
The reason behind that is because even if the user is inactive, there may stil be some NetBIOS traffic exchange between Sonicwall and the client and as a result the SonicWall does not consider that user as inactive thereby not triggering the inactivity timeout.
To overcome this, please follow the following steps :
Go to Users | Settings
User Sessions | Use: NetBIOS under “Don't allow traffic from these services to prevent user logout on inactivity”
NOTE: Forceful disconnect: If the SSL VPN client does not get disconnected manually from the client, but gets disconnected forcefully (may be Internet disconnection at the client end) SonicWall will not consider that user as disconnected but as an inactive user since SonicWall did not receive any disconnection request from the client. This time SonicWall will not show any NetBIOS traffic from the client as it is technically disconnected at the client side. In this scenario, the SonicWall might report "Auth Failed" in the logs due to multiple re-logings of the client. This user being an inactive user for SonicWall will still maintain the session under User | Status and will only be disconnected once it completes its inactivity timeout, set under SSL VPN server settings.