Ubuntu 18.04: unbound seems to stop working after a period of time

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

Only 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 . https://docs.pi-hole.net/guides/unbound/ https://discourse.pi-hole.net/t/pihole-on-ubuntu-18-04-with-unbound-fails-after-some-time/22585