I'm new to Affinity Photo, have the latest version installed and updated, using Windows 10 PRO, on an old HP Z800 running Dual Xeon 5570 with a crappy old Quadro P600, (AMD Radeon Red Dragon RX 580 8GB GDDR5 GPU on the way :D )...OK, on to the important stuff..lol.
I would just like to add I also get this happening without cropping or doing any resizing. I'm using a Nikon D850, large RAW files size, there has been no changes made by me in regards to settings, canvas size or anything in that regards. I noticed this after zooming in then back out, a white edge would appear (on any random side) and stay there, even after exporting. The image could be zoomed to 100%, move to the edge and you will see the white line there. It's really bothersome and has made me think I was doing something wrong and almost gave up with Affinity all together... I now "watch out" for it, which is tiring and should not be necessary. I'm going to delete and reinstall Affinity, see if it makes a difference (if any settings were possibly changed unbeknownst to me).
I will try to replicate this again, (maybe later today if time permits), and if you would like, I could maybe send the (NEF) file(s) for you to test. I would like to help resolve this long ongoing issue ASAP.. It seems there has been a number of us with this same bug...is it only Nikon files? I think all the reports I have read so far are with Nikon files, there's probably other manufactures as I didn't read them all..
Thanks for your help.
p.s. I'm enjoying editing with Affinity and really hope this minor bug can be resolved...sooner. :)