@dave1707, @John - the images are reversed in John’s skybox, and matched - see my crude tester image attached, the seams are only recognizably different with texture differences (my seamless tiles are great horizontally but poor vertically) . John have you specified all image inversions in your code instead of one?
@Bri_G I think the cubemap is correctly loaded into OpenGL but the shader is incorrectly sampling things, causing the mirroring issue.