DIAGNOSIS This is a navigation failure. The vSLAM camera or the infrared sensor on the top is dirty, or the room has low light, disrupting the robot's spatial mapping.
FIX Clean the circular lens of the vSLAM camera on top of the robot with a microfiber cloth. Clean the infrared sensor window next to it. Ensure the room has adequate lighting (at least 40 lux) for the camera to see ceiling features.
IF THAT DIDN'T WORK Delete the current Smart Map and create a new one. In the iRobot app, go to the map view, select the map, and choose 'Delete Map'. Run a clean-all cycle in mapping mode to generate a fresh, accurate map.
HEADS UP Highly reflective floors, very dark floors, or identical repeating patterns (like large square tiles) can confuse the camera and cause this mapping behavior.