Hi Gabe
Thank you for your reply. I have uploaded 4 files: _DSC0627.NEF and its .afphoto (this is cropped to square in camera and has the unexpected behaviour) and _DSC0587.NEF and its .afphoto. For the purpose of this exercise I simply opened the raw file in Affinity photo, pressed DEVELOP, then added an exposure layer and inverted it. I then saved the afphoto files with the history. You should be able to see that the nature of the exposure layer is different (it's icon is all dark) in the first file, where as with the second the behaviour appears normal (i.e. it has the white horizontal bars top and bottom). These are very large files so took a long time to upload from the middle-of-nowhere where I live! As a photographer I am new to affinity, so may have misunderstood how to load files in (particularly non-standard sizes). Thank you for your assistance.