Just tried replicating it on iPad Air 2 running the latest PB, all working fine. Tried rotating it any possible way and it worked as it should in any of the four possible positions. However, this might be more of a gyroscope issue, as if we rotate iPads when they are in a flat (horizontal) position, just lifting them up from a table or something, the gyroscope might fail to register a change. If you put it upright, however, things change.
Throughout the iOS 11 beta cycle some versions were better/worse for a regular screen rotation bug, when an iPad would get stuck in a landscape/portrait position. The latest beta seems ok, though.