the Australia walnut is a name I never heard from here. Genuine American walnut or asian walnut color is the best we use. The white lines seems to be the glues not treated correctly between the planks. we met similar cases before on laminate wood floors of walnut color, but it's easy to clean off if not all areas like this.
I had this issue with some art select midnight oak. Only few planks so took them out and swapped them over and hey presto fixed!