sudo error: problem with defaults entries

Issue

Every time when sudo is run, problem with defaults entries message is logged in /var/log/secure.

• Below error message is logged in /var/log/secure:

  Jan  3 01:13:45 server sudo[33111]: user : problem with defaults entries ; TTY=pts/1 ; PWD=/home/user ; USER=root ;
  

• Corresponding e-mail is sent to root's mailbox:

  To: root@server.example.com
  From: user@server.example.com
  Subject: *** SECURITY information for server.example.com ***
  Message-Id: <20230103061345.58B1F4003D08@server.example.com>
  Date: Tue, 3 Jan 2023 16:13:45 +1000 (AEST)
  
  server.example.com : Jan  3 06:13:45 : user : problem with defaults entries ; TTY=pts/1 ; PWD=/home/user ; USER=root ; 
  

• The same /etc/sudoers file is used on other hosts without error.

• Other than the above error message, sudo is working as expected. Users are able to run sudo correctly.