I had same issue of reports taking for ever and after 3 days of waiting - I finally got the CSV, only to realize the seem to have “Item Subtotal Tax” messed up (@randy - bringing this to your attention).
UPDATE: It looks like some issue on Amazon side - I tried downloading the report a second time and the issue remained and then retried again a few days later and the 3rd time was the charm and this time it got fixed.