If you remain signed into the forum but do anything on it (add posts, browse, edit) then it goes into idle state. If idle for more than a couple of hours, it signs you out.
If you close the forum and come back to it far later, next day, then the Remember Me should sign you back in.
It appears to be working for me with no problems so far on my IPad and doogie desktop.
I’ve probably just jinxed it, saying that :D