@chaker 

Hi,

By "power outage" you mean everything in your home shuts off, right?

If so, then could you please test what happens if you only power off the Archer AX55, but not the ISP modem? Does the port forwarding work or not after power to the AX55 has been restored?

  @chaker 

Ok. In this case I suggest the next time you have a power outage and port forwarding stops working you log into the Archer AX55 and note down its "Internet IP Address" (marked in the picture below). Then check whether that Internet IP address is a public IP address (which, as you probably know, is required for accessing your home network from elsewhere) or if it happens to be a private IP address.

  @woozle It definitely has the public IP:
 

It's visible in the panel as you pointed out, and also, when I try to access the public IP, on the port 443, the following page is shown:

(strange thing is, that it's only shown, when I am trying to access this public IP from my local network - if I try to access the port 443 from outside, it is unavailable)

BTW my firmware version is 1.4.1 Build 20250821 rel.70686(4555) now, but apparently, the issue remains in this version too.

  @chaker did you go to Advance --> System --> Administration --> And check local management via https is enable or not

  @Giang97 It is not enabled. Should it matter?

Thing is, I try to access the public IP (not the local one), just from the local network - then I see this screen from my AX55, when the issue occurs.

If I restart the AX55, port forwarding works again, and I can see the page from my actual server, when I try to access the same IP.

Therefore I am positive, that the AX55 has the public IP all the time, it's just the port forwarding, which is not working after both AX55 and my cable modem are powered down (e.g. due to power failure im the apartment).