So, the second TO had another problem. Neighbour bought powerline adapter from TP-Link which had active DHCP according to logs (I wonder if it was inactive till energy loss…).
2019-07-02 16:42:23 info dnsmasq-dhcp[5001]: DHCPREQUEST(br-lan) 192.168.2.149 b0:be:76:7c:a4:5e
2019-07-02 16:42:23 info dnsmasq-dhcp[5001]: DHCPACK(br-lan) 192.168.2.149 b0:be:76:7c:a4:5e TL-WPA4220
2019-07-02 16:42:30 warning dnsmasq-dhcp[5001]: no address range available for DHCP request via br-lan_2
2019-07-02 16:42:38 warning dnsmasq-dhcp[29742]: Last message 'no address range ava' repeated 1 times, suppressed by syslog-ng on turris
2019-07-02 16:42:40 warning dnsmasq-dhcp[5001]: no address range available for DHCP request via br-lan_2
2019-07-02 16:42:56 warning dnsmasq-dhcp[5001]: no address range available for DHCP request via br-lan_2
Problem solved by checking this (authoritative DHCP?):
I hope that TP-Link will behave normally after this.
Once again, thanks for your help!