Another thing I'd initially test: formatting hard/flash drive.
Try with a few albums to see if everything is loading up correctly and being read. For some reason initially, my NTFS drives weren't working with the BDP-1. The music would load on the BDP-1, but wouldn't play. So I had them formatted to FAT32 on Mac. You can go via "Disk Utility" and select the hard drive and "erase" a hard drive to a new format.
Also, depending on what format you use, start thinking of how to name your artwork. I typically drop one image into each folder titled "Cover.jpg"
It is spelled in the exact same way with the capitalized 'C' and 'jpg', not 'jpeg'....across all my folders. That way it works with Audirvana Plus or any software and the Bryston BDP.
(Although lately I've noticed that the BDP has cannibalized my " images and replaced it with its own versions with something like "bdp_front"...someone mind filling me in?)