Left side blind spot not working

Hi all, I recently purchased a 2020 Prius and noticed that (only) the left side blind spot monitor does not work, the passenger side works fine. The lamp in the driver mirror works because it lights up when the car is started, but it never lights up when there is a car coming up on the driver's side. There are no dash indicators of any problem, and a repair shop scanned all the systems and found no codes.

Any idea how to narrow down where the problem might be?