This may be a compound problem. We were upgrading PHP and may have had to restart apache several times in the process. This will totally bork your sessions. At one point, all PHP apps were borken, but Master Ra was able to rememdy things in short order. The other deal is the server processes huge tracts of spam every day, and SpamAssassin, doing its best, may bog the server down too. This should not cause threads to be marked unread though, just create lag on the pages. Could be a MySQL limit thingy, but I don't think so.
1. Is this consistently reproduceable? Can you follow a set of steps repeatedly to make this happen?
2. Is it still happening and when did it start?
(OK, so it looks like 3 questions but #1 is just restated twice)
(...and #2 has two parts)
Folks who are experiencing this should check into this thread with Browser/OS information, please.
I'm swamped today and may be able to have a look at it Monday. I also noted that there is a phpBB update (2.0.10) (actually several updates), but the notes do not mention anything about a problem like you guys are describing.
Apologies if this is making life difficult for folks. I know you rely on the tools to interact and we need to take care of it.