Stimulation coming in all directions makes things go haywire.
As the technology progresses, autonomous cars are getting better at distinguishing the difference between dangerous obstacles and harmless objects lying at the side of the road, but the computers still don't have the process down as well as most would like. Whether its traffic cones, the concave bottoms of soda cans at the side of the road, or an actual danger, the autonomous software getting loaded onto cars these days has a hard time knowing when to slam on the brakes or disregard the impulse.
To the eye of the radar sensors, the water jets and soap covered brushes of a car wash are an impending disaster.
Even in neutral, a car loaded with collision mitigation will hit the brakes and activate the pre-collision features, effectively stopping the car in the middle of the wash. Some automakers like Tesla have foreseen these sorts of scenarios and offer owners an easy way to shut off the assistants when going through a car wash. Others, like the Volvo XC90, require owners to delve deep into the owner's manual to figure out how to turn these systems off. In this particular case, the only assistant that made matters worse was Kia's Auto Hold feature, which isn't exactly a piece of autonomous technology. Once cars can drive themselves to the carwash for a bath, we're guessing the problem will be eliminated.