In iPad, the export preview renders completely wrong.
It shows a full green/red/blue layer depending on position of the pattern layer.
To reproduce:
open attached file
goto export>png>preview
1/4 size preview is show in one primary color.
if you use move tool to shift pattern layer by 1 in x or y position, the preview color changes to another primary color
it seems the preview does a sub-sampling and uses only pixels with odd x/y position for preview
same file renders correctly on Windows (muddy gray)
Update:
The file "preview 4" shows the 4 possible alignments in the 4 quadrants of a single document.
export previw wrong ipad.afphoto
ipad export preview 4.afphoto