animated object flickering in the background

hello,
here a cropped part of two following frames of a fullhd mattecar/people animation.
animation is rendered with medium animation preset and animation prepass/rendering.

foreground is good, but in the background i have some cars and people that get "partly “black” for some frames…(here a car in the middle of the picture)

what do you think, too bad light solution ?
thanks for a hint.

thomes
car01.jpg
car02.jpg

high animation preset fixed it…