Dotted line down through equirectangular 360 "skybox"

Hey folks, any of you got an idea as to why the following occurs?

Image of the problem: https://imgur.com/a/G6vWLqt

The equirectangular image is generated via Unity and is then exported as a PNG. The PNG file is loaded somewhat like this:

 var textureData = File.ReadAllBytes(path);

 var texture = new Texture2D(1, 1);
 texture.LoadImage(textureData);

 texture.Apply(updateMipmaps: true, makeNoLongerReadable: true);

If any of you have seen something like this before, any pointers would be greatly appreciated :-). Thanks.

Edit: I have seen https://forum.unity.com/threads/there-is-a-dotted-line-in-my-skybox-of-unity-2017-3.512171/ before, but as we load the image at runtime, we cannot change the importer.