Why does the Dropbox website keep logging me out?

I've had a Dropbox account for many years, and suddenly in the past few months it logs me out daily and tries to sign me into another unused gmail account.  I don't close the tab or the browser, it just goes to sleep.

Do I need to cancel the gmail account?  What can I do so I don't need to keep signing in?  Every time I do, my settings change.

And speaking of, is there any way to change the default settings of specific features?  Like I dislike quick view and would like the default to be full-screen instead of having to check the box again every time I log-in (again, daily at the moment...)

Thank you for your help!