Second Time - S2-E13
Character mistake: When Kiera is begging one of the Freelancers to send her back she says she could "prevent Liber8 from ever coming to 2077." She should have either said "coming to 2012" or "leaving 2077."
Family Time - S1-E9
Factual error: In the barn, one of the kids shoots Cameron, then drops the gun and flees. Cameron picks up the gun and checks how many rounds are in the magazine and then puts the magazine back in. However, after that, she pulls the slide back to chamber a round. But the semi-automatic pistol would already have a round in the chamber since it was just fired, and her action should have ejected an unspent round, which it doesn't.
Split Second - S2-E2
Revealing mistake: Shortly after Kiera drives the van past the train tracks, we see a few different shots of Travis and Carlos fighting. In a couple of quick shots, Travis' stunt double can be seen. (00:13:00)
Revealing mistake: When Travis dumps out the heads of the gangs leaders from the case, it is painfully obvious that they are computer generated.