1. Verify if the USB flash disk format is FAT32. If it's not FAT32, the upgrade file might not be readable, resulting in an upgrade failure.
Solution: Format and convert the USB flash disk format to FAT32, copy the files again, and attempt the upgrade.
2. Ensure the USB flash disk isn't mounted in the /mnt directory. As there are native files in the /mnt directory of the ONIE system, mounting the USB flash disk would overwrite them, leading to an upgrade failure.
Solution: Mount the USB flash disk to the /usb directory, or access the ONIE interface and utilize the Install OS method.