Hikvision ANPR issue

Hi
my customer has reported an issue where the camera doesn't always record Vehicles entering and leaving normally the later.
the other thing ive noticed is , when you and group of cars quite close it repeats the middle number plate even when you can see the correct number plate.
the camera in place is
Hikvision DS-2CD4A26FWD-IZHS
i'm assuming that it could be a case of tweaking something .

Regards
Eddie