Thirteen ways to divide the sky into twelve, and where they differ.
The twelve houses divide the sky around your birthplace. There is no single correct way to do it: some systems divide space, others divide time, and that choice shifts which house a planet falls in. Astrae calculates thirteen.
Equal House and Whole Sign divide the zodiac into equal parts -- simple and usable everywhere. Placidus, Koch and Regiomontanus divide the motion of the sky itself, which makes the houses unequal and, at high latitudes, unusable.
Above the polar circle some degrees of the zodiac never rise at all on a given day. Placidus has no answer there. Measured: it computes up to about 66.6 degrees, and no longer from 68. Astrae falls back to Equal House there and says so in the label -- a silent fallback would hand you a chart that looks right and is not.