In "The Ambassadors of Death": Episode 4, a UNIT soldier is killed when he touches the same barrier as the alien. In Episode 6, he's alive and well and back at work.
The blind of the rising communications monitor doesn't flip back again before it lowers, meaning the blue screen image stays behind as the monitor moves back down.
When Ralph Cornish(Ronald Allen) tells Taltalian(Robert Cawdron) "I told you to give the doctor full cooperation". in the viewer screen the actor's mouth does not move when he replies.
Many of the indoor sets are silvered, meaning the crew behind the camera are often seen moving in the reflections throughout the whole story.
Everything the aliens touch violently explodes, except the capsule, their prison, the gates and doors they open, and many other things that would be inconvenient to the plot.
The motion of the camera feed from the spaceship makes no sense unless the camera is free floating in zero G.
Liz walks through a boom microphone shadow as gives a mug of coffee to the Doctor.
Michael Wisher as John Wakefield says by mistake "The two craft will be licking up in a moment or two" instead of linking up.