Revealing mistake: We see Redfield's car strike the invisible barrier from a side angle. It jerks to a stop and the hood flies up, but there's no other front end damage - until the angle shifts to a forward view, a shot of an identical car that had been previously wrecked. Now there's suddenly considerable damage to the front end, and the hood is in a different, much more crumpled position.
Factual error: The colonists' planet has twin suns and, we're told, no night. We see the suns, side-by-side in the sky. But twin suns would not create perpetual day. Night/day is caused by the rotation of the planet on its axis, regardless the number of suns. In a binary star system, the two stars orbit each other around a central point in space. The planets would orbit around that central point too. In order for there to be no night, the planet would have to pass between the two stars, a process it would not survive. The gravitational forces of two opposing suns would tear the planet apart.
Continuity mistake: When Mr. Ferguson is measuring the wax figures, he's shown holding a tape measure up against the figure of Landru (the one holding the rope). In the next shot, the figure is shown with no one near it. The next shot again shows Mr. Ferguson measuring the figure.
Continuity mistake: During their conversation over tea, Mr. McKenzie tells the Ransomes about the other people aboard ship. One elderly couple, the Whiteaways, are sitting in the background in almost complete shadow - until McKenzie introduces them. Then we see them in sudden brilliant light, and they've shifted their seating positions relative to the table. When we cut back to the master shot, they're back in shadow and back in their original positions.