I noticed that the cookie (which I believe has the limit for when the forum checks the credentials again & does the redirecting) might not get updated even if you load/open pages in the forum. Which means that every 1 hour the credentials are checked and you're redirected away from topic pages to the main page.
I say this because just now when I got back to reply to Asyn's post, I was redirected although I visited the forum just few minutes ago.
Anyways, how ever the system may work, I suggest that the people responsible update the system so that links from e.g. emails, bookmarks, or page refreshes do go to the page intended, not to main page. Thank you.