I just got off the phone again with Customer Care. She told me that I was supposed to release the buttons before the screens would go black. I read her the instructions Customer Care had texted me on the first call:
"3. Continue holding [the buttons] for about 30 to 45 seconds, until the screens power down and you hear a chime. [my emphasis]" She said I had been sent incorrect instructions and had me go back to the car where she walked me through the reboot process.
Doing it her way didn't work, either, despite three attempts where she ran a timer to tell me when to release the buttons and pedal. She created a service ticket and told me that a technician would get in touch later today or tomorrow.
I asked whether they were getting a lot of calls about ADAS malfunctions since the 2.8.0 update. She was a bit evasive, saying only that they're getting "some calls about things not working since the update."