Well, I finally figured it out. The problem started about the first of the year, although I only just now realized it. It came with the forum upgrade to 2.0.2 on December 29, 2011.
I had the main forums page open in Firefox, carefully scrolled down so that the teardrops for all the forums would be just visible. I would reload the page once or twice a day. If a teardrop went dark I knew there was a new post in that forum so I would read the post to see if I knew anything that might help. Occasionally I would write an answer.
But if you are logged out the page reloads the same as before, except no teardrops go dark, even if there are new posts in the forum. For three months I did not realize I had been logged out and kept wondering why there were no new posts. I finally decided to ask here if there was something wrong with the forums, and that is when I discovered that I had been logged out. After logging in I discovered three months of new posts that I had been unaware of.
I participate in other forums and web sites where I must log in. They all just leave me logged in. Many even automatically log me in, realizing who I am from my IP address. If I have to log in every hour to use these forums it is too much trouble. Much as I love Scribus and try to help where I can, I'll just stick with the listserve and not bother with the forums from now on. One less Firefox tab to keep open.