I tried mapping it earlier from the gym to here, and there are at least three different hallways that seem to shift into place. The gym won't show up until there's at least four classrooms between them in one of the hallways, and the others have only three classrooms per streak.. they lead to various other places.

[Fishing out a paper from his jacket to read and be sure he's explaining exactly what he wrote, Oikawa gives Ken a mild grin.]

So, we could experiment with that to see where those other hallways go. It's definitely strange and totally changing on us, so you're not hallucinating.