When we're under heavy load (e.g. Freenode is netsplitting) our cache can get backed up. The cache is where your logs are served from when you reconnect a client.
At the moment we don't do a good job of detecting a slow cache and re-requesting from the primary log storage, but we're working on a fix for that, as well as improving cache performance so it doesn't get backed up as much.
It just so happened that there was a large split on Freenode earlier today, around the time you posted this message.