Gee from Denon wrote this last year:
It was felt that it would be much better if the unit used its Super capacitor technology to instead, perform a safe shutdown and eject of any USB media that was connected to the player. So, in firmware 1.0 which was the version used in all the production units, the big red screen and giant 10 second. Countdown was replaced by an onscreen icon in the top left corner of the screen which appears when the incoming power is lost and denotes when the player is performing a safe eject of the media.
USB media differs in how long it needs for a safe USB eject, as different media uses cache memory differently. some Solid State technology knows it’s better to write less frequency to the drive and so will often “store up” what could have been lots of individual writes, into one big, long write. A very full SSD could take longer than a Hard disk drive to finish writing data. For this reason, its best to use the emergency power handling capabilities of the SC5000 super capacitor as an emergency option only.