DOH Resolve: Context Deadline exceeded

Issue has occurred twice within last 2 days at approx 2:30pm. 

Queries time out from clients & from host running NextDNS CLI. 

Firewall: USG-4P
NextDNS Version: 1.37.2 (Have just upgraded from 1.36.0)
NextDNS Config:

control /var/run/nextdns.sock
cache-size 50MB
detect-captive-portals false
config e94ce2
max-ttl 5s
discovery-dns
use-hosts true
setup-router true
listen localhost:53
log-queries false
cache-max-age 0s
max-inflight-requests 512
report-client-info true
hardened-privacy false
bogus-priv true
timeout 5s
auto-activate true

Error from NextDNS CLI Logs

Sep 26 14:29:53 ubnt nextdns[11399]: Query 10.0.0.19 UDP A c.bing.com. (qry=28/res=12) 5140ms : doh resolve: context deadline exceeded
Sep 26 14:29:53 ubnt nextdns[11399]: Query 10.0.0.225 UDP 65 i.pinimg.com. (qry=30/res=12) 17177ms : doh resolve: context deadline exceeded

After stopping NextDNS CLI and starting again twice, issue resolved.

After running curl -svL https://dns.nextdns.io/info

About to connect() to dns.nextdns.io port 443 (#0)
*   Trying 103.212.225.153...
* connected
* Connected to dns.nextdns.io (103.212.225.153) port 443 (#0)
* successfully set certificate verify locations:
*   CAfile: none
  CApath: /etc/ssl/certs
* SSLv3, TLS handshake, Client hello (1):
* SSLv3, TLS handshake, Server hello (2):
* SSLv3, TLS handshake, CERT (11):
* SSLv3, TLS handshake, Server key exchange (12):
* SSLv3, TLS handshake, Server finished (14):
* SSLv3, TLS handshake, Client key exchange (16):
* SSLv3, TLS change cipher, Client hello (1):
* SSLv3, TLS handshake, Finished (20):
* SSLv3, TLS change cipher, Client hello (1):
* SSLv3, TLS handshake, Finished (20):
* SSL connection using ECDHE-ECDSA-AES128-GCM-SHA256
* Server certificate:
*        subject: CN=dns.nextdns.io
*        start date: 2021-07-31 00:00:00 GMT
*        expire date: 2021-10-29 23:59:59 GMT
* subjectAltName: dns.nextdns.io matched
*        issuer: C=AT; O=ZeroSSL; CN=ZeroSSL ECC Domain Secure Site CA
*        SSL certificate verify ok.
> GET /info HTTP/1.1
> User-Agent: curl/7.26.0
> Host: dns.nextdns.io
> Accept: */*
>
* additional stuff not fine transfer.c:1037: 0 0
* HTTP 1.1 or later with persistent connection, pipelining supported
< HTTP/1.1 200 OK
< Access-Control-Allow-Origin: *
< Content-Type: application/json
< Strict-Transport-Security: max-age=63072000; includeSubDomains; preload
< Timing-Allow-Origin: *
< Date: Sun, 26 Sep 2021 04:31:02 GMT
< Content-Length: 77
<
* Connection #0 to host dns.nextdns.io left intact
{"locationName": " Sydney, Australia", "pop": "gsl-syd", "rtt": 4483}* Closing connection #0
* SSLv3, TLS alert, Client hello (1):