I'm willing to bet this is simple, but it's not the first time I've encountered it.
I lay out an area, convert to seating layout and I get 3 rows of seats. We know that only two rows can fit - so, I've changed the size of the seating area, I've tried changing the row spacing... it will jump from 3 rows, to 1 row. I cannot get it to display 2 rows.