When Margaret, Ben and Hal (after saving Hal) sit on roof of the bus, soles of their boots are barely dirty. You can see dust on top of sole studs, but otherwise they are clean as if they just walked out of shoe store. One would expect dirty and muddy shoes in a war zone of destroyed city.
Previously, Lexi had been able to channel energy, radio waves, electricity, gravity, and on, but here they claim that in a vacuum, gravity doesn't exist. This is blatantly wrong on a few different levels, for one, and gravity isn't the only energy source available, meaning that Lexi should be able to wish the power core into the corn field if she wanted to.