NextDNS randomly erroring on unifyOS (UDM pro)

Github issue: https://github.com/nextdns/nextdns/issues/861

UDM pro: v3.1.16
NextDNS CLI: 1.39.4

DNS settings within GUI on UDM are set to ‘auto’ before NextDNS install.

On a clean install of unifyOS using the NextDNS installer command in sudo, the installation runs fine and installs successfully. All functions work as expected.

Installed using: 

sh -c 'sh -c "$(curl -sL https://nextdns.io/install)"

Status shows NextDNS running.

However, at some undetermined point where no restarts have occurred nor any GUI / CLI changes have happened. NextDNS begins to misbehave only with UDM’s own traffic.

All other clients routing traffic through UDM seem unaffected and resolve DNS queries with NextDNS without issue.

Within SSH, the ping command fails:

root@xxxxxx:~# ping google.com
ping: google.com: Temporary failure in name resolution

However, I'm still able to ping outbound IPs just fine.

root@xxxxxx:~# ping 1.1.1.1
PING 1.1.1.1 (1.1.1.1) 56(84) bytes of data.
64 bytes from 1.1.1.1: icmp_seq=1 ttl=61 time=6.01 ms

Checking the status of NextDNS states it is running.

root@xxxxxx:~# nextdns status
running

NextDNS log shows no stand-out errors apart from a lot of 'use of closed network connection' logs:

Sep 04 12:52:33 xxxxxx nextdns[32774]: Query 192.168.2.219 TCP 65 accounts.google.com. (qry=37/res=87) 21ms HTTP/2.0: write tcp 127.0.0.1:5553->192.168.2.219:15391: use of closed network connection
Sep 04 12:52:58 xxxxxx nextdns[32774]: Query 192.168.2.219 TCP 65 www.gstatic.com. (qry=33/res=90) 25ms HTTP/2.0: write tcp 127.0.0.1:5553->192.168.2.219:15419: use of closed network connection
Sep 04 12:53:22 xxxxxx nextdns[32774]: Query 192.168.2.219 TCP 65 xxxxxx-ats.iot.us-west-2.amazonaws.com. (qry=64/res=142) 10ms HTTP/2.0: write tcp 127.0.0.1:5553->192.168.2.219:15453: use of closed network connection

NextDNS config:

root@xxxxxx:~# nextdns config
setup-router true
auto-activate true
max-inflight-requests 256
cache-max-age 0s
report-client-info true
discovery-dns
mdns all
use-hosts true
profile xxxxxx
cache-size 10MB
log-queries false
max-ttl 5s
detect-captive-portals false
bogus-priv
truetimeout 5s
debug false
hardened-privacy false
listen localhost:53
control /var/run/nextdns.sock

A restart does not fix this and the only way I have found to make it work as expected is to uninstall, restart then reinstall NextDNS CLI. This however does not last longer than a day before breaking again.

Symptoms of this issue include not being able to access UDM remotely, UDM thinking there is no internet due to ping failures and speed tests within UDM failing.