DNS error_app?

The whole system works ok until last night, to say first: nothing has been changed regarding router-passwords-thermostat positon-internet provider .. from last night for no obvious reason mobile app lost connection to relay, so we uninstal app, restarted router and relay, all that time app simple just won't connect to previously used 2,4 ghz network with DNS error (with red cross mark) .. wifi signal is strong enough and we did not changed positions of router and thermostat .. anyone have similar issues?

thanks!