Water Plane material - strange issue on different size of plane

Hi
I have downloaded from marketplace “Water plane” where are blueprints with water plane materials. The Lake material is the best option for my purpose. Unfortunatelly, when I create a blueprints of this material and try to rescale it, it is working strangely. The material is working on small plane well , but when I will try to resize the plane, material go darker and on big plane is totally black. Do I have to rebuild the lighmap to fix this or do I have to change some value in the material? It is stupid question, but I can rebuild lightmap only during the night - computer is free to do it.