Might help if you posted which scanner you are trying. Do you have a link for it?
Note: I am not sure if we (@Merlin513 or I) have tried using USB Host with scanners
before. We have done most of our USB Host work on Teensy boards and I ported over
some of it here for the GIGA.
From what I can tell, this device is maybe just using USB Serial (CDC ACM) communications.
Have you tried our example: USBHostSerialToSerial? Did it show anything?
You might try turning on more debug information and see if that helps.
You can do that by editing the Arduino Library: Arduino_USBHostMBbed5 in src
the file dbg.h and change #define DEBUG
I think by default it is set to 0. You might try turning it fully on and set to 4 and see
if that gives any more hints.
Good luck