HTTP Session appears to expire

After a period, it seems as if the HTTP session expires.

Chat stops loading new messages, and no updates are displayed. Sending some text in chat causes the session to re-establish (although that chat message goes AWOL). Refreshing also works.

For example now, my oldest chat timestamp was ~ 40 mins old and said 151 players online. I hit F5, and suddenly it said 101 players online, and with completely different lobbies displayed.