The Royal We - S3-E2
Revealing mistake: On the RV of the guy being accused of molesting the girls, someone has written "PERVERT" in red spray paint. At a point you see Lightman next to a car, and the RV in the background, and the text is mirrored reading: "TREVREP", showing that during editing, this shot was flipped. (00:15:30)
Revealing mistake: As the RCV enters the gravel field with the bomb, you can see a person in shorts walking casually in the background, despite the area being sealed off.
Revealing mistake: Near the end, you're able to see the device used to blow open the kitchen door to make it look like a bomb went off. (00:34:55)
Episode #1.3 - S1-E3
Revealing mistake: When Lombard looks at Vera after realizing she stole his gun, the unruly wisps of hair are on his left temple, while in the rest of the scene they are on his right. The shot is mirrored, as you can see that suddenly it's like he's wearing a woman's shirt, with buttons on the left. (00:38:45)