PMG5617GA resets SSID and pass with electricity-cuts

Hi
PMG5617GA , firmware  V5.40(ABNA.1)C0.1

When a micro-cut is produced, the Wireless network turns off
SSID is set to "ZYXEL1234" and pass set to "ZYXELABCD"

However the 5G network --that I always have it turned off-- still keeps its SSID and pass

I'd like to know where that settings come from ( ZXYEL1234 / ZYXELABCD )
I reviewed all the settings but I didn't find nothing

Recently, my ISP installed a newer firmware in my modem
that firmware is newer that the last I found on internet.....it's strange

Could it be the firmware, who has that default settings ( ZXYEL1234 / ZYXELABCD ) built in?
or maybe the modem itself who is asking that settings to the ISP when the power fails?

thanks!