USG FLEX50W (20W-VPN) Factory Reset Not "5 Seconds" as stated in Manual

Last Saturday, I attempted to perform Factory Reset of USG20W-VPN, since it was compromised with unknown administrators in the User list, on older FW (prior to 5.39).

Below is from the manual (PG 912):

1I Make sure the SYS LED is on and not blinking.
2) Press the RESET button and hold it until the SYS LED begins to blink. (This usually takes about five seconds.)
3) Release the RESET button, and wait for the Zyxel Device to restart.
You should be able to access the Zyxel Device using the default settings.

I previously had held it 25 Seconds, with SYS LED not coming back on, and after releasing it began to flash. I rebuilt the entire configuration (thinking it RESET to factory), but suffered the same loss of service after two hours of deployment, due to suspicious activity in Session Log Wiz_VPN.

Today, I once again performed a Factory RESET, and low and behold after 35 seconds the SYS LED flashed while depressing the RESET Switch. I again rebuilt the configuration, without risking previous conf file might contain reference to bot.

Router has been running 1.5 hours, and traffic is pretty much flat lined, (which I would expect because office is closed). Don't beleive everything you read.