DIAGNOSIS The acoustic dirt detect sensor on the underside is either dirty or malfunctioning, causing false positives.
FIX Turn the robot over and wipe the small, round, microphone-like sensor (usually near the front caster wheel) with a dry cloth. Built-up dust makes it think it's constantly over debris.
IF THAT DIDN'T WORK The behavior is normal on rugs or uneven surfaces where the robot is working harder. If it's happening on bare floors and the sensor is clean, you can ignore it—it doesn't affect cleaning performance, just indicates the robot thinks it's on a dirty spot.
HEADS UP A solid red light, not flashing, indicates an error. Flashing red during cleaning is just the dirt detect indicator doing its (sometimes overly sensitive) job.