Apple Photos viewer splits my screen and I don't want it to
I'm trying to print some fine art photos from Apple Photos, but when I open an image I'm seeing only half the image, duplicated next to itself (i.e. the screen splits with the same half of the image duplicated on each side). Furthermore, they seem one two different edits of the same image! I've been using Photos happily since the unhappy demise of Aperture, and this has never happened before. And I'm a pretty heavy user. Anyone else run into this? I've attached a screen grab to make the issue crystal clear.
Thanks!