@terziyski 

Thank you very much for your thorough response.

I checked my router and I see that it is already configured as it should, or better, as you are suggesting. The only difference between your scan and the corresponding page on my router are that IPs (5 data fields) contain real IPs, not zeros. But I guesss that does not count in the problem. Or am I wrong?

So, much to my regret, this does not solve my problem. The problem is fixed, happens all the time and is 100% reproducible. And yes - with the previous, the old router I experienced no such problem. I feel quite frustrated just like I happen to be the first user ever to be affected by the problem of possible total internet black out if am not at home. How do people arround the world avoid the problem?

As it seems there is nothing to do in the Archer router management itself - no boot delay possibility, no scheduled re-booting  (not 100% sure), no other possible router missconfiguration -   I'm thinking of putting a mini UPS on the modem, what at my opinion should solve at least the short power outages. Next idea would be to put a delay relay circuit on the router 12 V power line. Any comment?

Kind regards, 

Tone42