ZyXEL Communications VPN Series Handbook page 734

Console Message
MONITOR > Log > View log
5 Make sure the version of the USB firmware is different from that of the
running partition. The device writes logs on the console and device log if
the firmware version is the same as the running firmware.
Console Message
MONITOR > Log > View log
6 This feature does not support the Device HA Pro firmware auto upgrade
to passive devices. Do not use USB firmware upgrade on devices with
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