Visible crew/equipment: After Raines shares details with Kellett about Semien's crew, when it cuts to Semien waking everyone up, just as he announces his contact with Belgian Federal Police, there's a visible T-mark taped to the floor behind Andre's cot. (00:24:25)
Nothing Sudden About It - S4-E3
Other mistake: The agent reaches into a toilet tank to retrieve a wristband. He holds the wristband up to look at it, and his hand isn't wet. (00:25:47)
Other mistake: Two FBI agents are speeding along a utility road trying to get to the airport and prevent a plane from taking off. They come across a closed steel gate in their way. They speed up the SUV and crash through the gate, and they get through as the gate breaks into many pieces. When their car gets to the airport we can see the SUV and there is not even a scratch on it.