>When I try to display the threads in a forum for a day, or display all the checked threads, the result is usually cut off, often in the middle of an HTML tag. It has been happening for a few days. Perhaps there have been other threads reporting the same problem, but I can't see them. The chatter forum may appear entirely blank in the upper pane, even though its first message appears in the lower pane as usual.

Have you tried to clear the cache and restart the browser?