If I watch closely, I can see some queries received during the time you circled.
The issue is likely the following:
WARN: Could not sendto() in send_dhcp_discover() (/__w/FTL/FTL/src/dhcp-discover.c:233): Network is unreachable
* Received 548 bytes from eth0:192.168.1.1
Offered IP address: 192.168.1.7
Server IP address: N/A
Relay-agent IP address: N/A
BOOTP server: (empty)
BOOTP file: (empty)
Message type: DHCPOFFER (2)
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You advertise Pi-hole's and your router's IP as DNS servers via DHCP. After the power-loss, your network clients renewed their DHCP lease and picked your router as upstream DNS server.
You should not set any DNS server next to Pi-hole as your clients will start using the other DNS server whenever they want. Only advertise Pi-hole's IP.