How do I prevent Texture2D.EncodeToPNG from creating artifacts on iOS?

So the problem was a simple one to solve. Basically the foreach loop going through "pixelList" in the code shown in the question above only writes to a subset of the pixels in the texture. I needed to initialize all pixels of the texture to clear before writing the pixels in the list.

The new code looks like this:

 ...
     
 Texture2D image = new Texture2D(imageWidth, imageHeight, TextureFormat.ARGB32, false);
   image.filterMode = FilterMode.Point;
   for(int i=0; i<Grid.UptPixelList.Count; i++){
     ClearImage(image, imageWidth, imageHeight);
     pixelList = Grid.UptPixelList[i];
     origin = Grid.OriginList[i];
       foreach(UptPixel pixel in pixelList){
         if(Mathf.FloorToInt(pixel.position.z - origin.z) < 0) continue; // Skip, we've gone underground.
         image.SetPixel(Mathf.FloorToInt(pixel.position.x - origin.x + halfWidth), Mathf.FloorToInt(pixel.position.z - origin.z), pixel.color);
       }
     image.Apply();
     
     File.WriteAllBytes(filename + Path.DirectorySeparatorChar + dirname + layerCounter + ".png", image.EncodeToPNG());
     
     layerCounter++;
 }
 Destroy(image);
     
 ...

Where ClearImage is:

   void ClearImage(Texture2D image, int width, int height){
     for(int x=0; x<width; x++){
       for(int y=0; y<height; y++){
         image.SetPixel(x,y,Color.clear);
       }
     }
     image.Apply();
   }