Seeing large bright ball-shaped reflections from the sun on vehicles when driving. What could be causing this?

You said it Joyclimber...
" Reflections from the sun"

Or it could be just the sun hitting the cars just at the right angle to produce a bright glare. Have you noticed this with certain type of vehicles, such as the backs of SUV's or back of box step trucks that have back windows?

I've noticed something similar myself, the bounce of the sun off a vehicle. I found wearing sunglasses helped a lot.

Some drugs will do this too

Check your blood pressure. This can cause flashing orbs in peripheral vision.
Halos around lights can be cataracts. Floating images or black spots can be retinal damage. Finally, make sure the windshield is clean.

Catarracts, glaucoma, eye issues.....
Or, it could be the sun came out.
Can you elaborate, explain your mysterious question?
Who is seeing what you have so vaguely described, and is it only in the daytime?