Hi all,
I am experiencing the very same behaviour of Affinity Photo (1.8.4 on macOS 10.15.7).
As it seems, the coordinate system of the window in which the file is opened is somehow messed up: Other than expected, the coordinate axes have unit vectors [-1,0] and [0,-1] instead of [1,0] and [0,1]. Pixels with positive coordinates are in the upper-left quadrant of the coordinate system, not the lower-left. The contents of the opened file appears as if rotated about 180°. Despite the erroneous display an export of the just opened file will be fine and oriented correctly.
In the screenshots attached you can see that the window's set up is not ok. Also attached is the file that causes this behaviour. It seems that images of a small size in width and height will cause it.
Icon.OK.afphoto