There was a problem with the session cookies that had caused some users to get randomly logged out.
Today, I finally isolated that bug and fixed it. It was actually in one of the root system configuration files and was randomly impacting users on this and all of our other sites. So if you had selected "Remember Me" during the login process, you normally wouldn't need to keep logging in every time you visited. But this bug would cause that setting to get lost once in a while.
As you can imagine, being semi random made it very difficult to find. But once the pattern was detected it only took a few hours of forcing the error to popup before the solution was found.
Hopefully, if you use the "Remember Me" switch, you shouldn't have random logout issues any longer. But if you do, please report them to me right away.