Time limit exceeded: last error: NS dara.ns.cloudflare.com. returned SERVFAIL

So apparently my latest certificate renewal hasn't gone through yet, even though my config has worked for about 2 years straight now.

The message in the docker logs is as follows:

 time="2022-06-17T21:47:14Z" level=error msg="Error renewing certificate from LE:
{*.xxx.com [xxx.com]}, error: one or more domains had a problem:\n[*.xxx.com] time limit exceeded: last error: NS dara.ns.cloudflare.com. returned
 SERVFAIL for _acme-challenge.xxx.com.\n" ACME CA="https://acme-v02.api.lets
encrypt.org/directory" providerName=default.acme

What is causing this SERVFAIL message and what can I do to fix it?

Huh. So I use a pi-hole for DNS. For the majority of time I had been using Quad9 upstream DNS servers. Within the past 1/2 months I had been having some issues with them, so I switched over to Cloudflare. I just tested switching to OpenDNS and the certificate renewal went through. So it seems there was something up with the Cloudflare DNS servers