XDJ-XZ Unable to update firmware - MASTER REC blinks

I have an XDJ-XZ that otherwise works fine.  However, when I try to update the firmware by pushing and holding the USB1 STOP and RELOOP/EXIT, while powering the unit on, (with no USB stick in the port) screen displays ”Connect USB storage device into top USB1 port.” for a hot second, screen blanks out and the MASTER REC light start to blink.  I'm able to reset this by pulling the power cord and switching the unit off.  The blinking stops within 30 seconds or so and then able to restart the unit without issue.  Any solutions or alternative way to update the firmware?  Thanks.