Factual error: As the X-Men land in Cairo, scenes reveal the destruction Magneto is wreaking around the world, where it is simultaneously daylight in New York, Sydney and Cairo - it is possible for it to be daylight in two of these locations at once, but not all three.
Factual error: When Apocalypse touches the television in Cairo and says he is "Learning", the next shot shows the rooftops with many smallish satellite dishes in view. This is set in the early eighties when satellite dishes for TV were much larger.
Revealing mistake: When Apocalypse first introduces himself to Magneto in the factory and tries to persuade him to join his side, a seam in Apocalypse's facial prosthetics next to his mouth is starting to come apart during a close-up shot.
Erik Lensherr: Does it ever wake you in the middle of the night? The feeling that one day, they'll come for you? And your children? Charles Xavier: I feel a great swell of pity for the poor soul who comes to my school looking for trouble.