Bump. Well I don't have an answer but I've found out how to easily reproduce and characterize the problem.
First, this is all within the default Photos app. I haven't installed another image viewer so I don't know if it's even more generic.
The problem occurs when the image being displayed has an aspect ratio that is close, but not exactly equal, to the screen's native 16:9.
When the image is just slightly taller or wider than 16:9, then Photos zooms the image to Fill instead of Fit, partly cutting the image at the top and bottom, or sides (depending on whether the image was taller or wider than the screen's native 16:9).
I can easily reproduce the bug by doing the following:
- take a picture (camera defaults to 4:3 aspect ratio).
- Edit the picture in Photos.
- enter the Cropping tool
- open the list of preset aspect ratios and choose 5:3.
- Done to exit out of editing.
5:3 aspect is slightly taller than 16:9. With the image displayed correctly you would see black space on the sides of the image. But instead the image fills the screen and the top and bottom of the image are cropped off.
Interesting corollary:
- revert the image to original.
- Edit and Crop again, but this time choose 3:2 aspect.
3:2 is slightly taller than 5:3.
The image will still be displayed incorrectly (Filled) by default, however now you can pinch zoom-out to get the image fully displayed (Fitted). This is impossible at 5:3 aspect. However, if you swipe to a different image then back to the 3:2 image, it will again be displayed incorrectly.
From 3:2, the next taller preset aspect ratio is 7:5. At 7:5 and taller, images display correctly by default (Fitted not Filled).
The bug also occurs on the opposite side of 16:9. There aren't any preset aspect ratios but you can reproduce similar behavior (clipping of the sides instead of top & bottom) by manually cropping an image to wider aspect than 16:9.
I hope Apple sees this and fixes it soon!