Slave Island - S1-E7
Plot hole: After Storm's attempt to escape the Genoshan prison is thwarted, she ends up in the ocean right at the shoreline of the beach, where she is captured by a Sentinel. Aside from the fact that it makes no sense for a Sentinel to be hiding in the ocean in the event that a mutant tries to escape the prison, there is absolutely no way that a two-story tall robot could hide in the ocean right by the beach, as the water would be way too shallow. You can even see that the water level only goes up to the Sentinel's ankle area when it is standing upright in the ocean. (00:03:15)
Suggested correction: Perception. (1) The Sentinel isn't as close as it appears. If it were close, then she would have been caught in its waves as it emerges. Also, she would be looking only at its chest circle. It's several yards away. (2) She washes ashore. She fell from the sky. She couldn't have fallen from that great height into shallow water without hitting bottom. (3) It's also a two-story tall robot. Its weight would sink it into the sand. So it could have very well been down that deep.
Eyewitness - S1-E12
Continuity mistake: When the immortal who's trying to kill Tessa snipes at her in Duncan's car, his shot shatters the passenger-side window. When Duncan tails Tessa and her police escort to the safehouse, the passenger-side window is intact. (00:30:05 - 00:35:50)
The Tale of the Whispering Walls - S2-E7
Factual error: Betty Ann is supposed to be telling this story on a Leap Year night with a full moon. While it's necessary for the plot, the most recent Leap Year with a full moon was in 1972, and is calculated to happen in 2048 next.