Just like I described in title, Sankey chart could show just blank(white) stripe for some data
here is a example table
Create table abc(a string, b string, c string, d string, e string);
insert into abc values('a1', 'b1', 'c1', 'd1', 'e1');
insert into abc values('a1', 'b1', 'c1', 'd1', 'e1');
insert into abc values('a2', 'b1', 'c1', 'd1', 'e1');
insert into abc values('a3', 'b2', 'c1', 'd2', 'e2');
insert into abc values('a4', 'b1', 'c1', 'd1', 'e1');
insert into abc values('a4', 'b2', 'c1', 'd2', 'e2');
Here is Sankey chart of all data and counts in looker