In the episode "God's Equation", Lisa is seen with an "alien head" tattoo on the back of her right shoulder. This completely disappears during her talk with Allie during the hostage situation at the encounter meeting.
The episode "Acid Tests" is set in 1970, and it involves two alien hybrid twins who are said to have been born in 1959; yet, the corpse of "Larry" is at least sixteen years old because the sheriff makes reference to the fact that Larry started using his powers at that age. A birth year of 1949 would fit perfectly, however, indicating that this is a dialogue error.
At the end of "Maintenance", the last day shown is November 8th, 1980. When that date first appears on the screen, it is daylight. Then we see Eric waiting for Becky to get out of her house (in order to live with her to Maine), it is then night time. When she doesn't go out he decides to hit the road back to his military base and finish packing up. When he enters the base, it is daylight again. However, when he finally takes off to Maine, while he is on the road, it is night time again and the date shown is still November 8th, 1980. It should be November 9th (or later) since at least one day and a half separates the scene when that date first appeared and the last scene it appears in.
Lubbock, Texas is portrayed as being hilly and wooded with lush meadows. Lubbock is very flat and has no indigenous trees, only shrubs (grassland is also scarce due to the small amounts of rain the region receives).
At the beginning of the episode "Maintenance," during the recap, a scene between Captain Marty Erickson and the adult Eric Crawford is shown which was not shown before in the mini-series. Either it was intended to be shown after the recap during the new episode, or was a deleted scene from a previous episode.
In the episode "Maintenance," Jesse looks at a newspaper that has a headline "Ambassador to El Salvador disagrees with Pentagon". However, the story carries a byline of "New Delhi" and talks about a meeting between the prime ministers of India and Pakistan. It also mentions "Prime Minister Atal Bihari Vajpayee", even though the scene takes place in 1980 and Vajpayee would not become PM of India until 20 years later.
In "Jacob and Jesse", when Major Crawford is shown photos of the "contacters", one of his assistants walks back and forth through the light beam of the slide projector without the picture on the screen being disturbed.