During the big battle at the beginning of the show at the Production Facility, the conveyor belt is stopped. In a faraway shot you see it still moving and the next shot it is stopped again.
When Julie is rescued by the Resistance at the Visitor Security headquarters, Stephen is seen walking with Diana behind Julie and Martin. Several shots later he is shown standing next to the building, and later he is seen arriving at the building again along with Diana.
When Daniel is letting Elias into the Medical Center, he is not wearing his gold collar and gold armband on his uniform. Later, when Daniel harasses some medical students, he is wearing the gold collar and armband. And still later, when Daniel is brought to Security Headquarters with Brian, the gold collar and armband are missing again.
When Kristine Walsh is on the Mothership looking for Sean in the Special Section she leaves the key she got off Donovan in the door lock several times, yet it seems to be back in her hand in the next scene.
The Visitors' vulnerability to firearms seems to be tied to the needs of story, rather than anything substantial. SOmetimes firearms work on them; other times; they don't.
When Kristine Walsh is on the Mothership looking for Sean in the Special Section she leaves the key she got off Donovan in the door lock several times and yet it seems to be back in her hand in the next scene.
At various points throughout all 3 parts of the Mini-Series, the vocal reverberation effect that is supposedly one of the only ways a Visitor can be detected as not human is either very low or completely missing from the sound mix. This is present on both the original 1984 broadcast as well as the DVD release.
In the final shot of stars out of the mother ship's front window, reflections of the sound stage lights are clearly visible.