I have noticed some results of different tests.
If you put a number in a cell then fill down with that single cell, it only fills into the visible rows.
If you put a letter into a cell and fill down, it fills down a series into the visible rows only. Same thing with dates.
If you have a column of data with some rows hidden and you select the column and Delete, it only deletes the visible data.
If you have a column full of data, select it (click on the colun letter), then look at the automatically generated COUNTA at the bottom of the window, it only counts the visible rows. Same thing for the other functions. This might be the answer to your problem, just ensure all visible rows have data in that column. You can drag the result up to your table if you need it to be part of your table.