Please follow the below template, it will help us to help you!
Expected Behaviour:
Pi-hole running on raspberry pi as DNS and DHCP for local network. OpenVPN is also installed where remote clients use Pi-hole's DNS. Has been working fine for a while.
Actual Behaviour:
DNS is running fine for remote VPN clients, but DHCP and DNS server is no longer serving local network. It seems like Pi-Hole is partially using the OpenVPN 'tun0' interface instead of 'eth0', but I can still access the lighttpd web GUI. Any help would be greatly appreciated thank you.
From your debug log, some errors shown. I would run pihole -r and select reconfigure to get Pi-Hole on the correct interfaces and IP's.
** [ DIAGNOSING ]: Networking
[✓] IPv4 address(es) bound to the tun0 interface:
10.8.0.1/24 does not match the IP found in /etc/pihole/setupVars.conf (https://discourse.pi-hole.net/t/use-ipv6-ula-addresses-for-pi-hole/2127)
[✓] IPv6 address(es) bound to the tun0 interface:
fe80::4122:aad5:47aa:621e does not match the IP found in /etc/pihole/setupVars.conf (https://discourse.pi-hole.net/t/use-ipv6-ula-addresses-for-pi-hole/2127)
^ Please note that you may have more than one IP address listed.
As long as one of them is green, and it matches what is in /etc/pihole/setupVars.conf, there is no need for concern.
The link to the FAQ is for an issue that sometimes occurs when the IPv6 address changes, which is why we check for it.
[i] Default IPv4 gateway: 192.168.0.1
* Pinging 192.168.0.1...
[✗] Gateway did not respond. (https://discourse.pi-hole.net/t/why-is-a-default-gateway-important-for-pi-hole/3546)
I removed "PIHOLE_INTERFACE=tun0" from /etc/pihole/setupVars.conf which shouldn't have been there, and ran pihole -r with the repair option followed by a reboot.
That is all it needed to get back up and running, thanks for pointing me in the right direction @jfb