“Car tried to turn left into oncoming traffic, driver had to avoid collision,” wrote a customer of Waymo, the unit of Alphabet, in early March after taking a ride in one of the company’s experimental self-driving taxis in suburban Phoenix. The customer was referring to the human backup driver who sits behind the wheel and is supposed to take over if a potential safety problem arises.

According to internal Waymo data reviewed by The Information, there were several technical problems on that ride that caused the driver to take over twice: The Waymo minivan robotaxi got “way too close” to another car, moved “super slow” at one point, made an “unnecessary” lane change and, lastly, experienced the apparent near-collision. Despite the close call, the customer gave the ride four stars out of five.

The majority of the several hundred Phoenix area residents who ride in Waymo’s robotaxis, which are considered to be the most advanced of their kind, have nice things to say when their rides end. But close to 40% of the time in data reviewed by The Information, passengers registered a complaint through the company’s mobile app.