Perhaps stop cheaping out on the cameras and procure those with high dynamic range. Then again those may be "expensive and complicate the supply chain with for a small delta"

But then, again, what is the point of the radar?

Lidar would make it pretty obvious whether it's a sign or a car, even if the camera didn't tell you. The part where the lidar doesn't bounce back at vehicle level would be a dead give away.

A approaching incline has entered the chat.

Approaching inclines aren't exactly hard to interpret from lidar either.

A human driver slows down and moved their head around to get a better view when the glare from the sun is too strong to see well. I’d expect a self driving car to similarly compromise on speed for the sake of safety, when presented with uncertainty.