QuickSight Analysis Export to Excel Limit

Documentation seems to state that QS can export data up to 1,000,000 rows. When attempting to export an analysis with 650,000 rows - the export shows as being "Limited to 100,000 rows" when exporting to Excel. The same export to a CSV file works, with the maximum row count of 1,000,000 applied. Is the Excel export actually limited to 100,000 - or is that limit being applied somewhere else? Many thanks!