HI @hodain ,
I don’t know exactly what’s happening, but it seems to me, that it’s not simply the Mirror Modifier, that’s causing it, but the compression from 32 bit EXR to 8 bit PNG.
Also the change from sRGB, to Non-Color makes a difference.
door_normal, sRGB:

door_normal, Non-Color:

door_texturing…, sRGB. Doesn’t fix it:

I don’t have access to Substance Painter and I haven’t watched all of these Lessons, but it seems to me, that the problem occured somewhere after Importing to SP.
After Baking in Blender and Applying the Mirror Modifer, everything was still okay, as far as I can tell.