When Kimberly (Pink Ranger) first exits the water in the mine/quarry her hair is dry.
When Billy drowns the team never attempted to perform CPR. If CPR did work on Billy then Zordon may have been free. Billy's "death" was caused by more than drowning, including Rita's magic (you can clearly see a deadly magic effect on his body) and the abrupt, forced plunge into the water. Furthermore, his neck could have been broken by the chain. While the drowning was certainly part what happened, it was not the only thing that caused him to die. CPR could have been a solution for the drowning, but certainly not the other factors that resulted in his death. Furthermore, Zordon being free would not have mattered in the long run; he even says that "there can only be one Red Ranger."
When running from the zord in the black rangers original attempt to control it, Alpha 5 pauses mid run (this can also be seen in the trailer) in what seems like a CGI error.
When the car gets hit by the train, its rear axle gets torn off, but when the car comes to a rest, the rear wheels are still attached.
When the teens are swimming through the subterranean lake, while they are nominally swimming down/sideways towards the cave with the ship, the bubbles they're exhaling move "forward" from their face, revealing that they're really facing up, and the effect is being accomplished by altering the camera orientation.
When the Rangers are driving away from security, the tail lights on the van are off and then back on when the camera cuts to the front of the van and then the rear again.
In the scene right after sam's brother flips the truck over, the camera shoots from red ranger's view, we can see the steveston whale watch shuttle bus facing south, but in the next shot we see the bus flipped facing north, clearly indicating it was shot on two different days.
At the beginning of the film, the caption reads 'PLANET EARTH: CENOZOIC ERA', and what appear to be pterosaurs can be seen flying in the background. The Cenozoic is the current geological era, and pterosaurs went extinct in the Mesozoic.
When Rita goes to the jewellery store she tells the assistant to hand over her necklace. The assistant starts to take it off but in the next shot it is no longer round her neck & Rita is already holding it.
When they are in the ship with Billy's dead body, the position of Trini's arms varies between shots. In some they are folded, in others they are by her side.
In the scene when we first see the morphed rangers from the back walking towards the cliff edge to see the gold monster marching towards the city, their helmets from the back can be seen having two pieces, but when the camera shows them from the side with their faces visible, the helmets are one piece.
The end credits of the "making of" documentary on the home video release include a credit for "Abby Road Studios." The first word should be spelled "Abbey."
When Trini cliff jumps as the rangers are discovering their powers, Kim can be seen and heard beginning to say "What is wrong..." as the other rangers are shown running up to join her. The camera then focuses on Kim and she says the full phrase "What is wrong with you!" over again and in a different tone of voice.
When Billy calls to his friends from the water, Trini (Becky G) is seen laughing and turning around. The angle changes and she's seen standing facing forward with a flat face, while the next angle change has her laughing and turned around again.
Trini is forced to repair the walls of her bedroom as a punishment by her family (specially by her mother).