Early on in a driving scene the 1967 Plymouth Belvedere patrol car is seen instead of the '69 the officers are driving.
When Reed is just about to make a U-turn, he is about to cut off a white vehicle behind him. In the next shot, from the opposite direction, when Reed is actually making the U-turn, a blue vehicle is behind him. Even if it is meant to be the same vehicle, the blue vehicle comes into frame much later than it should have in relation to where the white vehicle was seen through the police cruiser windshield.
The "dime bag" girl says the ice cream truck has pictures of popcorn on the side. It does not.
After a foot chase, Malloy tackles the alleged drug buyer and pins him to the ground after a brief struggle. The camera then shows what is supposed to be Malloy's perspective over a hedge of Reed arresting the ice cream truck driver. Malloy, being crouched over his captive, would not have been able to see over the hedge.
Reed comments that the ice cream truck doesn't have commercial license plates. Yet upon arrival, it's clear that the ice cream truck driver has been standing in front of the license plates obscuring them from view.
When Reed spots the ice cream truck as Adam-12 is driving down the road, the truck is about a half-block away. There is no way he could tell, at that distance, that the vehicle has license plates for a personal vehicle and not commercial as it should be.
As Reed and Malloy were driving away after talking to the girl about the ice cream truck, the film fluorescent lights were reflected off of their patrol car.