The main question is: why do my Deco X20 devices lose their internet connection after restarting the ISP modem, despite the "Smart DHCP" option being disabled?

My home network consists of one modem from my internet service provider and two Deco X20 units connected to the modem with an Ethernet cable each of them and operating in Access Point mode.

A year ago, when I first set up the network, I noticed that after restarting the ISP modem (e.g. after a power outage), the Deco devices would not connect to the internet again - even though everything seemed fine on the modem (I even tested this by turning on modem WiFi and connecting to the modem - internet was there). Then I read that I had to disable the "Smart DHCP" option, which I did, and everything worked as it should.

Until a certain moment, when suddenly a few months ago the problem returned... I thought I had accidentally enabled the Smart DHCP option, but it was still disabled. Unfortunately, it now looks like this: every time when the ISP modem restarts, I have to repeat the entire procedure of restarting the entire network so that Deco provides internet, i.e.: I turn off Deco, turn off the modem, turn on the modem, turn on Deco and only then do I have internet.

I thought it was because of the lack of Deco updates, because until yesterday I had 1.0.6 Build 20220909 Rel. 59388, but today I updated to the latest 1.2.1 Build 20240723 Rel. 64983 and the problem did not go away. I also checked again: I have the "Smart DHCP" option disabled, and despite this, when I restart the ISP modem, the signal does not return and I have to restart the entire network.

What should I do? Unfortunately, I have no idea how to deal with this problem. I would attach a log that I recorded from the moment when I turned off the modem to recreate the problem, but this forum apparently doesn't allow me to upload log.