I haven't logged in for years. There are a number of things which could be causing your problem.
You need to stick to one of the five 'sites'. If you try to access a different 'site' it will require a fresh login.
If you log in using different devices, you need to have the multiple logins box ticked in Site Settings.
If your computer is not configured to accept and store cookies, it will insist on a fresh login each time.