one problem I had was the speed of writing to my USB flash drive because of the default timeshift settings.
Steps to resolve (Using windows ten laptop).
1. shut down your zgemma box and remove USB stick.
2. put disk into your windows 10 laptop and press cancel when the format dialogue appears
3. press WIN +R for the run box and type in "cmd" and then press enter. This will bring up a command prompt window
4. type in "diskpart" and enter, a new administration cmd window will appear allowing you to modify your disks.
******** FOLLOW THE NEXT INSTRUCTIONS VERY CAREFULLY, a MIS STEP CAN DAMAGE YOUR WINDOWS INSTALL OR PERSONAL FILES *****
5. type "list disk "and press enter, this will show you a list of detected disks on your computer.
6. Identify which disk is the disk number of the USB flash drive (In your case it will be the 64gb drive), and type "select disk <disk number of the USB"
7. type list partition and press enter, confirm that this is definitely the disk you wish to wipe.
8. type "clean" and press enter
9. type "create partition primary" and press enter
10. type "select partition 1", press enter and then type "format fs=fat32 quick" and finally type active and press enter.
you can now remove your usb drive from your laptop, plug it back into zgemma and start the box.
after this, you are free to initialize the usb within your zgemma again. The final step I do is to disable timeshift from timeshift settings.
what you have done is wiped the partition map of the USB drive and started again.
This works for me and hopefully may work for you too.