Munin: Graph not plotting one label

The problem is that your numbers add up to more than 200, while your graph is max'd at 200. (Have you recently added CPU to this instance?)

Telnet to the munin-node port (4949) and look at the output of config cpu, possibly the result of --upper-limit on the third line:

graph_title CPU usage
graph_order system user nice idle iowait irq softirq
graph_args --base 1000 -r --lower-limit 0 --upper-limit 400
[...]

If there's something in there that's limiting the graph to only 200%, look in the munin config files (usually /etc/munin-node/plugin-config or the like) to see if it's accidentally hardcoded.