User error of some type. If clean and you set it up as they instructed,there should be no problems. It's a pretty simple system. Got lump, good air flow, and fire? That thing should spin the temp dial.
I'd say the roasting will take about 20 to 30 minutes but you need to monitor temps as you roast it. I'd pull at 110 and let it rest on a rack under tented foil. Get the egg up to 600 and sear that puppy on all sides. Your Looking for a final temp around 130-135 after a final rest. Remember that the temp will increase while at rest, so I'd Make sure you pull it from the searing stage prior to 130.