I use Simplify3D to control an Airwolf HD2x as well as a Lulzbot TAZ 4, and it looks like both of them have been experiencing this issue.
What happens is that while the raft is printing, it will be printing the first layer completely fine, and then all of a sudden, it's like the extruder goes completely off the rails and just doesn't turn back around to continue along its predefined path. On the Lulzbot, I'll occasionally hear a gear noise like the extruder is suddenly retracting a lot of filament very quickly. It basically ends up doing this: https://drive.google.com/file/d/0B5Y2Iz ... sp=sharing
Then when it comes back from its journey to nowhere, the filament has retracted and it takes several more lines of air-printing before it stars coming out of the nozzles.
I'm not modifying anything in the G-code, so I can't figure out how a few changes to the default speed settings could be causing this kind of error. I'd blame the machine/firmware if it weren't happening consistently on two different machines. Anyone have any insight?