DIAGNOSIS The robot's camera-based navigation was obstructed or confused, often by low light or highly reflective surfaces, causing a mapping error.
FIX Don't edit the bad map. Delete the current map from the app's settings. Run the robot on three consecutive "Mapping Runs" in the daytime with all lights on. Keep pets, people, and moving objects out of its way.
IF THAT DIDN'T WORK Clean the camera lens on top of the robot with a dry microfiber cloth. Even a faint smudge can distort its view. Also, ensure there are no direct sunlight beams or mirror-like floors in the skipped area.
HEADS UP Never pick up and move the robot during a mapping run. Let it return to the base on its own each time. Moving it corrupts the map data.