The uniform worn by the state trooper early in the film has regular shirt buttons in earlier shots, then metal buttons in latter shots.
A police officer, alone, would not search two suspects and check the trunk of their car, without calling for backup first, or at least handcuff one and detain him in the back of his cruiser.
After pulling over the black car and pulling up in front of it, the officer walks to the rear of the car to check the license plate. The front plate is clearly visible from when he stopped in front of the subject vehicle.
Sanchez fires off many shotgun blasts without ever reloading.
When Shane finds Tia in the trunk of the Triad's car, he instructs the young male to call the cops. He should have instructed him to call EMS/911. He then takes Tia into the car getaway car.
When the Chinese commandos sneak up on the headquarters at night, they carefully step off the boat and wear camoulflage makeup as they stalk through the dark. One thing - they have bright flashlight beams attached to their weapons that would make them visible from a mile away.
The note Shane reads in the rain, and later steps on (in the rain) is clearly coated because it does not break down.
Several times during the final battle Shane breaks arms and hands of several of the Duda, including the Colonel (the sound of breaking bone is clearly heard) yet seconds later they are all able to use the same hand or arm to fight and shoot weapons.