When exporting an artboard that is placed on subpixel (i.e. its X or Y coordinates are not an integer), the suggested artboard size on export is 1px larger than the real dimensions.
Steps to reproduce:
Create new document. Check 'Create artboard'. Set page width and height to 100px
Select artboard, duplicate it, place the new artboard on X:120.5px, Y:0
Rename the new artboard to 'Artboard2'
File > Export. Select PNG. Select 'Artboard2'. The suggested export size will be 101px x 100px.
The same behaviour can be seen when exporting with Export persona. If the artboard is placed on round pixel dimensions (X:101, Y:0), the export size is correct.
Please re-open the issue because sub-pixels value affect print exports.
Test case: (1) create an artboard of 20 × 20mm for print, (2) add a rectangle the size of the artboard and fill it with a color, (3) export the arboard as jpeg or eps.
What you'll get is 1 extra pixel on right edge and 1 at the bottom edge. It's because the 20 × 20mm artboard translates to 236,22 × 236,22 px and the 0,22px need and entire pixel to fit. I understand how .jpeg could be an issue, but please consider the following use cases:
exporting for some CNC where precision matters
having an eps that some other designer could use as a linked/embedded/placed file
creating a logo package
I'm thinking that having a bleed might fix part of the issue, but it's highly impractical when you consider that designers often grab (select) things from one artboard and move it to their working artboard. In this case you might not notice the bleed.
I really enjoy the Affinity, I even gave up on every Adobe product I had, but this issue is a real bother. Please let help me find a Real solution, one that considers every point I raised earlier.
P.S.: The files I was working on when I discovered the issue.