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[ 391.326493] imx2-wdt imx2-wdt.0: Device shutdown: Expect reboot!
[ 391.333590] Restarting system.
Battery voltage: 3973 mV
Is the above restart the result of you pressing and holding the power button for 20 seconds or more?
It does not look like what I would expect if it was, it looks like a "warm restart" rather than a "cold restart (full reboot)".
It is only the "cold start" start-up code the can recognize an image file and load it, a "warm restart" does not.
An additional indication of failing to do a full "cold start" is if the file is still on USB storage afterwards.
The "cold start" code will always delete the image file.