Rate causes high CPU usage
The rate package that provides the breakdown of which ips are using how much bandwidth on the traffic graph seems to peg the cpu.
It also happened on 1.2.3 with the Rate package installed. It was solvable by removing the rate package (no longer possible as it's built in).
The CPU is loaded enough that the web interface responded very slowly and the gateway statistics reported packet loss.
It does not seem to always happen however as it was fine for days on 2.0-RC1 and weeks on 1.2.3 before it had a problem.