Corrected entry: When Steven is making his escape at Visitor HQ, he runs through a room full of dead Visitors, most of them slumped in their chairs. This indicates that they have been killed by the red dust. But if that's true, then the room would still be contaminated, and would kill Steven and his colleague before they got any further.
Corrected entry: In the first two episodes, the Visitor HQ was protected by a laser fence, which had to be powered down from the inside before Julie could be rescued. Yet in Part 3, the Resistance simply run across the front lawn and attack the HQ. What happened to the fence?