In The Long Earth, when the protagonists first run into the Gap:
"I don't think it was the stepping." Sally rubbed her own stomach. "It was the weightlessness. And then the sudden return of gravity. It was like falling."
"Yeah. It really happened, didn't it?"
"I think so," Sally said. "We found a gap. A Gap in the Long Earth."
Then, shortly after Lobsang appears,
Sally was furious. "How did you manage to hit a vacuum on Earth?"
Lobsang sighed. "Sally, we stepped into a place where there is no Earth. A total vacuum, interplanetary space. ..."
When I reached the first quote, I read it to mean what Lobsang later confirmed, that the "Gap" is a missing Earth in the Long Earth. That's presumably why she said "Gap" in the first place. But her question to Lobsang makes me think she didn't think it was a missing Earth after all. Since she did say, specifically: "How did you manage to hit a vacuum on Earth?", with emphasis by the authors.
This feels like a discontinuity in the narration - as if Sally realised what had happened, named it the "Gap" with a capital G, and then immediately forgot what happened.