I posted this issue on http://forums.dds6qkxpwdeubwucdiaord2xgbbeyds25rbsgr73tbfpqpt4a6vjwsyd.onion/t/whonix-virtualbox-15-0-0-4-9-point-release/8076 but this thread is probably the right place for this.
Assuming it is permissions, I tried to run
from the command line and got the same results as expected. Then, I tried
but that doesn’t show the USB drive.