@KarlLegion per your request, separating this bug report into it's own topic.
Reproduced in Affinity Photo V2.0.3 on Windows 10. A sample project is attached that demonstrates the problem.
A simple test reproduces the bug:
drag a 200x200 white square into a 210x210 canvas
scale it to fill the canvas with all pixel snaps on
You can see the fractional coverage bug in the gray artifacts at the upper-right edges and corner:
Workarounds are very awkward; you have to overscale by 1 pixel (or disable pixel snapping and drag a fraction of a pixel past the edge). That means snapping is worthless, basically. The bug occurs on many other resolutions as well, but not all. When the resolution is high, the translucent fringe pixel is often as little as 50% covered. It's particularly nasty in high-res projects because you don't notice the fringe unless you zoom way in.
scale-snap-bug.afphoto