From my understanding - Sony is investigating a few claims of where some USB drive were recognised before but not now after the Marshmallow update. I dont really know too much about this issue im afraid.
Any chance you can reply back with more information:
What brand/model drives they are?
Did they definately work before the update the Android 6 (Marshmallow)?
Have you tried using different USB ports?
Have you tried a factory reset - you never know, it might work?
