Just wrote a lengthy comment and when I tried to post I got the message I was not logged in...BS I was logged in. Think it got dumped due to content!
Got to save your log in and click the remember me button. It times you out if you don't do that. If your typing something lengthy the forum has a time limit for inactivity if you haven't done that and after so much time of inactivity it will automatically log you out. So if your typing something long and click post you might lose your post mattering on how long it took you to type it if you haven't set your log in like that.
To stay logged in type your password in wrong in the log up top. It will redirect you to a new page. Log in from that page and make sure to click and check mark the "Remember Me" button. Then you won't experience that problem anymore. Just remember to use that on your next log in.