Cookie Problem / Being Forced to Logout
Apologies for not picking up on this sooner. The problem is nearly always related to your locally stored cookie in your web browser. I've just changed the cookie prefix so everybody will have to login again, and that'll store a new cookie, and should solve the problem.
Here is how to fix it your end in the future though:-
Login to the forum, then click log out. You'll get a message saying your cookie related to the forum has been erased. Then close the web browser down fully, start it up again, login to the forum (remembering to check the box "remember me") and that'll store a fresh cookie with no issues related to it.
If that doesn't work your web browser isn't letting the forum erase your cookie. So you can manually erase it. I'd need to know what browser you use to help you do that though.
You can also use the auto-restore feature if you lose anything you've typed on the forum for whatever reason. If you logged back in, went to start a new thread again, and look in the bottom right hand corner of the message area you should see the wording 'restore post' which will restore your post. You've probably seen the yellow box pop up when typing a long post about every 20 seconds saying "auto saved". So it'll pull up the last saved point. You might end up with a couple of sentences missing on the end.
Though as I've said before over the years, it's not a forum problem, it's browser and operating system related in 99.9% of all cases.
Make sure you keep your browsers up to date. And to test if it is your browser, try using another one just for 10 minutes and see if that kicks you out, I bet it doesn't (unless it's using the same cookies).