Export to Excel Missing Data

I know this is an old post, but I have just spent hours puzzling over this problem and managed to solve it.  In my case, it was because on the grid I was exporting I had identical rows.  I spotted this by putting a counter on the page and looking at how many rows were shown in the grid.  When I saw something like 17 rows in the counter, but only 16 rows on the grid, I just looked closely at the data and could see there were rows with duplicate data, even though they were distinct rows returned by my query.

To solve the problem, I just added an Index column to my query https://stackoverflow.com/questions/45715963/creating-an-index-column-for-power-bi), added that to the grid and changed it to not summarise.  Hope this helps someone!