This is what the sword looks like in the Sunstance Painter viewport:
And i've exported with the sketchfab and PBRroughness presets, both yield the same problem:
The surface won't stay flat. I've uploaded this way before, but never had this problem. I guess the only thing i did differently this time is moving the normal map into the layers in SP, so i could edit out some artifacts. Does that change anything? Though, it didn't help to hide the layer normals, and use the TextureSet normals, the problem still persisted.
Here's what the normal map looks like in that area, if you want to look: