It looks like your machine is losing position. This is commonly caused by over-tasking the stepper motors, which causes "lost steps". Since it's an open-loop system, there's no way for the Shopbot to compare commanded position with achieved position; it just keeps going, assuming it's in the right place. It could be that your rapids are too fast, that your acceleration is set too high, that you're taking too heavy a cut, or that there's a mechanical problem with your machine, like couplers slipping, debris in the racks and rails, or a failure of lubrication. Another thing to check is cooling and heat-sinking on the drives - problems that start out after the machine warms up often are due to electronics getting too hot.