In Power query, the load preview by default is 1000 row. By default, the column quality also only looks at the first 1000 row. You can verify this by the status bar at the bottom of the Power query window. To change the profiling so it analyses the entire column of data, select the profiling status in the status bar. Then select Column profiling based on the entire data set. https://theexcelclub.com/data-profiling-views-in-power-query-excel-and-power-bi/