Will deactivates the Robot while he's right by the ramp entrance to ship. After that, in the wide shot of the chariot in front of the Jupiter II, he's nowhere in sight, presumably due to the reused footage from the original pilot when the Robot wasn't part of the crew.
When Penny hops on the jetpack, she is not wearing the safety harness. When the view cuts to the long shot (the takeoff), it's suddenly around her.
As the Robinson family travels in the Chariot, the exterior wide shots show the entire family wearing fur-lined parka coats while riding inside the vehicle. However, whenever the camera cuts to the Chariot's interior closeup of the family, none of them are wearing their coats.
In scenes showing the rear of the Jupiter 2 (where the chariot is being loaded in preparation for the journey south) the hull is segmented, quite different in appearance from the smooth, seamless hull of the front (door) side.
When the cyclops is throwing boulders at the chariot, the second boulder is exact same as first boulder both in appearance and where it lands, though the second boulder somehow rolls towards and hits the chariot.
When checking the Robot's circuits, Will plays chess with it, and uses the move "Queen's bishop to King's Knight Four". That move is impossible, as King's Knight Four is the opposite color as that on which the Queen's bishop moves. The Robot later said "Does not compute" to at least one other move, but not to this one.
When Don tests the newly set up force field by shooting a laser at it, he turns facing the field straight on and slightly crouches so that his gun is located about mid-chest as he fires. However, the laser beam begins from the top of his head instead of from the tip of his gun.
When John and Don were entering the cave to escape the giant they bumped into the side of the cave and the rock material moved like foam rubber.
To wear parkas on a brightly-lit soundstage had to have been uncomfortable for the cast. In some of those "cold weather" scenes, facial sweat is visible (e.g., Don's face prior to the first cyclops encounter).
When Don, Judy, Will and Penny are trapped in the ancient ruins, Don exclaims "It's an earthquake!" but the quality of the sound is different from his normal voice and the movements of his lips and jaw do not match the obviously dubbed-in dialogue.
When John performs his first jet pack takeoff, the source of the smoke is seen to be pipes attached to the stage floor.
During the intro sequence, a crew member's reflection can be seen in the chariot's glass while Will is working on it.
Prof. Robinson decides the family must head south when he discovers the temperature in the area of the ship will drop to 150° below zero, resulting in everyone freezing to death. But the spaceship is designed to travel through outer space, where the temperature is more than 400° below zero. It would be much safer to just stay in the space ship.
At one point the Robot says the creature is 16 meters tall; it appears to be much taller than 50 feet. However, production stills of the 2-foot-long Chariot miniature, posed near the actor in the Cyclops suit, show that the creature was only a bit over 3 times the height of the vehicle. That would make the monster about 21 feet tall, clearly a lapse between the script and the special effects team.