Yes, that is only option in Joomla, but it might be related with your existing 3rd party plugin which can reset the user login session data .
The session handler is set to 'database' not 'php' so not sure if this makes a difference?
To be honestly, I am not really familiar with this, but base on what i know is 'database' option for those user session data will stored in this table #__session.
If you set to 'PHP' option, it will stored those user session data to text files on your server, but i am not sure what is the different between this, perhaps you can try set to 'database' option and see how it goes.