Its likely the Device is in “Autodetect” USB mode. On the PC the files are transferred in MTP mode.
WHen its connected to the Prius, it only supports MSC mode, hence no files.
THe solution is to erase all the files. You can do that by Formatting.
then set the USB mode to “MSC” and transfer the content in that mode.
Then when you connect to the Prius all the files will be there.
