Cookies are what determine if you are remembered or not.http://www.whatarecookies.com/
The setting on the forum hasn't changed and neither has the cookie name.
I would usually advise clearing caches and reset your devices settings and see if it resolves itself
I had a quick look through logged issues with this forum version and it looks ok ..
if required I can rename our cookie - which will force all users to lose their saved logins (and view settings) and set them again
This forum is "timed". All forums are. They have to be.
A session is created everytime you login and the server will hold it open for a set period of time . If there is no activity for a set period of time, i.e. you decide to go the shops or fall asleep, then the server will close the session. If this didn't happen, then eventually there would be overload and the world would end.
Our session timeout is sufficiently long enough so you can type huge messages (there is no interaction between server and your machine until you hit "submit"). it's 4600 seconds, which is around 1 hour and 16 mins