That look like motion blur, and it also look as a cloudy day, so that make it harder.
I just done the same on my drive today, all the footage from when driving in sun are fine ( 80 / 80 km/h highway speeds ) but as soon as the sun went behind one of the rain clouds then my plate captures dropped significantly to almost none.
Then again you are driving pretty slow there and passing non moving targets, so yeah i think i would have expected more too.