OK solved it now!
The image has to have a data size less than 50Kb for the controller to be able to download and process.
Took a bit of messing around and tweaking in GIMP but got it down to 24Kb and now it loads.
Can someone tell me what day the NodeBB metrics start on? Is it a rolling past 7 days or is it Monday-Sunday? Or something else?
@dennismsmith the graph in the ACP?
It's a doing 7-day graph. You're able to customize the view by clicking on "custom date range"