This appears to be the root cause of your problem. Don't do this.
As you noted, when you have your DHCP server provide multiple DNS options, clients are free to use any of them and some (or all) of the DNS traffic bypasses Pi-hole.
Your debug log shows that the active interface on the Pi is not responding to DNS traffic. That is at least one of the problems.
*** [ DIAGNOSING ]: Name resolution (IPv4) using a random blocked domain and a known ad-serving domain
[✓] fish.muted.io is 0.0.0.0 via localhost (127.0.0.1)
[✗] Failed to resolve fish.muted.io via Pi-hole (192.168.0.102)
[✓] doubleclick.com is 172.217.166.46 via a remote, public DNS server (8.8.8.8)
*** [ DIAGNOSING ]: Networking
[✓] IPv4 address(es) bound to the eth0 interface:
192.168.0.102/24 matches the IP found in /etc/pihole/setupVars.conf
*** [ DIAGNOSING ]: Setup variables
PIHOLE_INTERFACE=eth0
IPV4_ADDRESS=192.168.0.102/24