[VMG8924-B10A] Factory Reset as a result of Power Outage?

What kind of settings did you change in your test?

I notice that 1.00(AAKL.24)C0 is not the latest firmware of VMG8924-B10A.
Maybe you could give it a try with the latest firmware to see if the problem still happens or not.

I also ran a test with the same 1.00(AAKL.24)C0 firmware.
I changed the password of admin account and WiFi SSID and then powered it off for several times. I can still use the new password to log in the WebGUI and the SSID is not reset to default value.

If your problem still can't be resolved after trying the latest firmware, my suggestion is to contact Zyxel local support because it seems like a single case problem.