Yeh worst so far for me tonight. Sometimes got a message my session had timed out but only off looking at another tab for a cupla minutes. Maybe look at the session timer settings, increase it a bit? I can see you would not want to leave someone logged in for 6 hours without activity. Oh, maybe the software is not seeing the activity?
Give it a squirt of Marvel Mystery Oil
session time is set to 15 minutes of inactivity and then you get logged off. That is pretty standard and has been this way for years. It is not always 100% 15 minutes there can be other things happening that may end your session early but they are rare.
I am not sure why t would say your session expired if you were only away for a couple of minutes, but keep in mind session clock starts from when you load a page from the site and not if you are just reading or scrolling the page etc.
The Remember Me function is something different where a Cookie is stored on your Computer or Device, under the control of your Browser settings, and when you request a new page from the Forum if it comes back with you need to Login, it looks for the Cookie and using your name and password stored in that to automagically logs you in.
In the case of DD, Sarge and others it is this automatic login that has gone haywire after I made a change for security reasons and then reversed 12 hours later when it started causing people problems.
I will have another look around and see if there is anything at all in the software I can do to clear it up.