I set up pi-hole with unbound on my ubuntu 18.04 machine. I followed the instructions by pi-hole.
Clients can reach websites with this method but after some time I get timeouts. Pihole is still forwarding requests to 127.0.0.1 but it seems that unbound doesn't answer anymore. Even on the host machine I get timeouts.
dig pi-hole.net @127.0.0.1 -p 5353 ; <<>> DiG 9.11.3-1ubuntu1.8-Ubuntu <<>> pi-hole.net @127.0.0.1 -p 5353 ;; global options: +cmd ;; connection timed out; no servers could be reached
systemctl restart unbound solves this problem. Unbound is still running and doesn't show any obvious errors though.
I posted on the pi-hole forums and added quite some information there so you might want to check the thread .