Without seeing what has gone into making your graph, its difficult to answer your question. Most generators in Designer generate tileable, seamless patterns. Look back through your graph and see where you have introduced a non seamless element (e.g. have you used a bitmap image). Once you have located the element(s) causing the issue then you can use the tools to make the material tileable, turning on tiling in the 2D view can help with this.
Dave