When the family leaves to look for Dr. Smith, the entrance to the Jupiter 2 is clean and neat and there is a short ramp to enter. When they return the entrance is covered with rocks and branches, like when they first landed. It appears to be reused footage.
After Dr. Zachary Smith eats some fruit, he grows in size. His clothing also increases in size (including such things as his shoes, belt, belt buckle).
When Professor Robinson and Major West interrupt Dr Smith's shower, they scold him and tell him to get back to the ship for a meeting. Smith's hair was still full of soap, and he no longer had access to the shower. In the next scene, Smith is back at the ship, with his hair clean and dry. No explanation for how Smith managed to rinse the soap out of his hair.
John states that the pituitary gland is located at the base of one's nose, when it is actually located at the base of the brain.
John stated the outside temperature was 145, down from 147. He and Don then proceeded to go outside and work on the water conservation system. An average person who is at rest, wearing minimal clothing, with 10 percent relative humidity and drinking water constantly can avoid overheating in temperatures as high as 115 degrees Fahrenheit. Even assuming John and Don have a higher tolerance for heat, they would not be able to survive in temperatures as high as 140F for more than a minute or two. Later, given an unspecified temperature, though undeniably hot and likely similar, all of the Robinsons, Don, Dr. Smith, and Debbie all go outside in search of water with no protection from the heat.
When Maureen is talking to Dr. Smith (from Smith's view) her shadow is seen behind her, but there is no shadow from the giant sized Dr. Smith which should extend over Maureen.
As Professor Robinson was prying the rock off of Don the rock could be seen giving way as if made of rubber or foam.
The fruit is supposedly responsible for making both Debbie and Doctor Smith grow to three times their normal size, but no explanation is given for the source of the additional body mass nor the fact that Smith's clothes appear to have expanded as well.
No explanation is given as to why the rainfall on Smith would reduce him back to his normal size.