Shift Into Turbo: Part I - S1-E1
Plot hole: Divatox and co. live in a submarine in Angel Grove lake. In "Hogday Afternoon", Angel Grove lake was drained to about 30ft at the deepest. The lake would have to be several hundred feet deep for a large submarine to hide there.
Plot hole: Everything in the Youth Center is in hieroglyphics because of the magic staff. Look carefully at the arcade machines in the background - the writing is still in English.
Passing the Torch: Part 2 - S1-E19
Plot hole: In the first episode of series 4, we are told that the Power Chamber was directly below the Command Centre. In Hogday Afternoon, part 2, at the end of series 3, the Command Centre was completely destroyed - so how could the remains of the Command Centre be next door to the Power Chamber?
Answer: The Rangers are human. Blue Centurion is a robot/cyborg.