These stars are in a small bubble of free space, almost completely surrounded by the larger bubble of Col 70 sector, which is permit-locked. It's like a glass jar with a narrow neck; the "bubble" of space inside is quite large, but the way in and out again is relatively narrow. You can't approach it from sideways, or from behind. The route plotter fails because it can't figure out how to calculate such a large deviation around the permit-locked stars.
We do no know why the Col 70 Sector (and a couple of neighbouring sectors) is permit-locked. It was not always permit-locked. We assume it's because of the Thargoids; they've hidden something Thargoidy in there, and don't want us to find it yet.