Black texture shows using WWW on Android phone

So I'm trying to load in a texture, stored on the phone's internal storage. I get the path of the file as follows:

 string[] filePaths = Directory.GetFiles(m_FileDir);
     if ( filePaths[0] != null )
     {
         StartCoroutine( ImportFile( filePaths[0] ) );
     }

I'm pretty sure that bit works as within the co-routine I added an output for the width and height of the loaded texture, which is correct.

The code inside the co-routine is:

 WWW www = new WWW( "file:///" + _dir );
 yield return www;
 
 m_Text.text = _dir + " \n " + www.texture.width + " \n " + www.texture.height;
 
 Texture2D tex = new Texture2D( 4096, 1271, TextureFormat.ETC2_RGB, true );
 
 www.LoadImageIntoTexture(tex);
 
 m_Mesh.renderer.material.mainTexture = tex;
     

I looks like it should be correct, but it only produces a black texture.

Any help would be greatly appreciated.

EDIT:

The other textures in the scene are 4096:xxxx and setting the aspect ratio of the texture2D to 2048:635 also produces a black texture. Testing on a Samsung Galaxy S5