WordPressの常時SSL化を無効にできず、Let’s Encryptが更新できない

前提・実現したいこと

今回、ホームページのSSL認証が期限切れてしまったので更新しようと試みました。
ですがエラーが発生して更新できないため、「まず常時SSL化を無効にしないといけない」と判断しました。
ところが常時SSL化を無効にすることができません。

発生している問題・エラーメッセージ

# sudo certbot renew
Saving debug log to /var/log/letsencrypt/letsencrypt.log

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Processing /etc/letsencrypt/renewal/mail.○○○○○.xyz.conf
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Cert not yet due for renewal

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Processing /etc/letsencrypt/renewal/○○○○○.xyz.conf
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Cert is due for renewal, auto-renewing...
Plugins selected: Authenticator webroot, Installer None
Starting new HTTPS connection (1): acme-v02.api.letsencrypt.org
Renewing an existing certificate
Performing the following challenges:
http-01 challenge for ○○○○○.xyz
Waiting for verification...
Cleaning up challenges
Attempting to renew cert (○○○○○.xyz) from /etc/letsencrypt/renewal/○○○○○.xyz.conf produced an unexpected error:
Failed authorization procedure. ○○○○○.xyz (http-01):
urn:ietf:params:acme:error:unauthorized ::
The client lacks sufficient authorization ::
Invalid response from http://○○○○○.xyz/.well-known/acme-challenge/RDWsE0qBwX19XxNJiPp-QTepEbZsBWGQC9DKhRS2i0M [139.162.82.132]:
"<!DOCTYPE HTML PUBLIC \"-//IETF//DTD HTML 2.0//EN\">\n<html><head>\n<title>404 Not Found</title>\n</head><body>\n<h1>Not Found</h1>\n<p". Skipping.
All renewal attempts failed. The following certs could not be renewed:
  /etc/letsencrypt/live/○○○○○.xyz/fullchain.pem (failure)

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

The following certs are not due for renewal yet:
  /etc/letsencrypt/live/mail.○○○○○.xyz/fullchain.pem expires on 2019-10-28 (skipped)
All renewal attempts failed. The following certs could not be renewed:
  /etc/letsencrypt/live/○○○○○.xyz/fullchain.pem (failure)
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
1 renew failure(s), 0 parse failure(s)

IMPORTANT NOTES:
 - The following errors were reported by the server:

   Domain: ○○○○○.xyz
   Type:   unauthorized
   Detail: Invalid response from
   http://○○○○○.xyz/.well-known/acme-challenge/RDWsE0qBwX19XxNJiPp-QTepEbZsBWGQC9DKhRS2i0M
   [139.162.82.132]: "<!DOCTYPE HTML PUBLIC \"-//IETF//DTD HTML
   2.0//EN\">\n<html><head>\n<title>404 Not
   Found</title>\n</head><body>\n<h1>Not Found</h1>\n<p"

   To fix these errors, please make sure that your domain name was
   entered correctly and the DNS A/AAAA record(s) for that domain
   contain(s) the right IP address.