please see this bug reported in Windows - it is found in Mac, AFPUB 1.10.5.
This still plagues me every time and, strictly speaking, there is no way to avoid a host of pre-flight photo proportion errors and, worse, photos that appear to be no longer adhering to their original aspect ratio.
https://forum.affinity.serif.com/index.php?/search/&tags=afb-4723