I would think that either you’re having problems with the electrical connections to your flash disk, or that your flash disk itself may be marginal. It’s also critical to make sure that the Domino and USB device has a stable +5V supply with the ability to source as much as 500mA (To make sure there’s always enough power). I’ve tried various USB drives/SD card readers and there were a few that didn’t work well, especially some of the cheaper ones. Depending on how you’ve connected the USB devices you may want to try shortening any wires from the USB device and Domino. Can you try other USB devices like mice, keyboards, etc. to see if they are properly recognized?
-Larry