Diagnosis
The robot is likely in a 'spot cleaning' mode or has a calibration error from a previous incomplete run. The default behavior for a new session is a systematic back-and-forth pattern.
How to Fix It
First, power cycle the robot. Press the power button on the side for 5 seconds to turn it off. Wait 10 seconds. Press it again to turn it on. Place it on a flat surface and press the 'Auto' button once. It should now attempt a standard, rectangular cleaning pattern.
If That Didn't Work
The cliff sensors on the underside are obstructed or dirty, causing erratic navigation. Wipe the four black sensor windows on the bottom perimeter with a dry microfiber cloth. Ensure the robot is not on a very dark or pure black floor surface during this test.
Heads Up
If the robot consistently spirals, it indicates a failed gyroscope or mainboard. This requires manufacturer service.