This means NAV gets a "400 BAD REQUEST" error when attempting to contact your graphite-web server for a graph rendering request, which means you should check the logs of your graphite-web server.
We have done extensive debugging on this, and our graphite server is not the culprit.
NAV generates a call to <nav server>/graphite/render?format=json&from=-5min&until=now This is the first of many calls to /graphite/render on the device pages. All the other calls to /graphite/render looks to be working.
best regards
Andreas Dobloug USIT/UiO