Just found out this issue when trying to re-export all my scenes using 2px padding instead of 1px to get rid of visual glitch.

I have a scene background with 2048 width, exporting to 2048x2048 texture. Under polygon packing, the export will failed with paddingX, paddingY set to 2 even if EdgePadding is set to false. If paddingX, paddingY set to 1, will export will be fine. However, in Unity there will be visual glitch ( lines ) so I think I need it to be at least 2.

I am using rectangle packing to work around the problem but if possible, I hope this can be fixed.

Sample Project:
Spine Polygon Packing Issue.7z

Weird. I tried on another scene which also has a background of 2048px wide. However, it can export using polygon with even 5px padding correctly.
Looks like something is wrong with the uploaded one here.

I took a look at the export and found that setting the padding to 1px actually give me a packed image with no padding (empty space) between the sprites. I guess that explains why when I have padding set to 1px (Polygon Packing), I still see the artifacts in game.

Here is the packed image with padding = 1 (Polygon Packing):

and here is the packed image with padding = 2 (Polygon Packing):

You can see that padding =1 actually has no padding. On the other hand, padding =2 give me 2px empty space between sprites.