A FAT32/UEFI formatted USB KBE will not be able to contain files larger than 4gb due to the limitations of the FAT32 file system.
There are currently two methods of resolving this issue:
1. Use 2 USB drives; one loaded with a "bootable USB flash drive image of the Boot Environment" and the other loaded with a "bootable USB flash drive image of the System Image" Both of which can be downloaded from the Details page of each respective deployment.
2. Use Legacy/BIOS instead of UEFI (if that's an option) and format the drive as NTFS