Factual error: When the boys are sent back to the Cretaceous era, they come across a leptictidium, a small, bipedal mammal they call "Leppy." Leptictidium were not around in the cretaceous, they didn't appear until around ten million years after the dinosaurs went extinct, in the early Paleogene. They also lived in Europe, not North America.
Here There Be Monsters - S1-E10
Plot hole: The female police officer has a theory that Johnny was the Strangler in the case the papers claimed he helped solve but this hardly makes sense. If she was researching him as was seen in the episode, surely it would have said something about Johnny being in a coma during the bulk of the murders since the story was about Johnny.
Forever Red - S1-E34
Plot hole: Tommy states that he and the other Zeo Rangers destroyed the Machine Empire's leaders and ultimately destroyed the Machine Empire except for the Generals who escaped. This is not true - Lord Zedd and Rita destroyed the Machine Empire leaders at the end of series 4, and the Space Rangers destroyed them again in Countdown to Destruction in series 6. The Zeo Rangers never destroyed the Machine Empire.
Suggested correction: How would Tommy know that? He didn't watch the show or know the ins and outs of what happened in space. This is what he believed based on his experiences on Earth. Everything you described is factually correct, but Tommy did not witness this. So, to his knowledge, he destroyed the Machine Empire.
Revealing mistake: Air Force Colonel Owen Crawford and his two personal assistants are poring over classified intelligence files in the Colonel's office. When they start to review a slideshow of photographs, one assistant sets up a projector screen and turns off the office lights as the other assistant switches on the slide projector. Photographic images immediately appear on the screen in the background, but the first assistant is still standing directly in front of the slide projector in the foreground. Not only does he not eclipse the projected image on the screen, but no projected image appears on the assistant's body. Obviously, the images on the screen in the background are projected from another source far off-camera. (00:48:50)