Mailman lists are missing from cPanel

Symptoms

cPanel is accessed to work with existing mailing lists but they do not display in the cPanel user interface.

Description 

There are a few reasons why mailman lists may not be showing in cPanel and one of them is due to one of the lists being corrupted. This is able to be seen by executing

/usr/local/cpanel/3rdparty/mailman/bin/list_lists

and provides an error output 

# /usr/local/cpanel/3rdparty/mailman/bin/list_lists
Traceback (most recent call last):
File "/usr/local/cpanel/3rdparty/mailman/bin/list_lists", line 136, in <module>
main()
File "/usr/local/cpanel/3rdparty/mailman/bin/list_lists", line 102, in main
mlist = MailList.MailList(n, lock=0)
File "/usr/local/cpanel/3rdparty/mailman/Mailman/MailList.py", line 133, in __init__
self.Load()
File "/usr/local/cpanel/3rdparty/mailman/Mailman/MailList.py", line 722, in Load
raise Errors.MMCorruptListDatabaseError, e
Mailman.Errors.MMCorruptListDatabaseError: [Errno 2] No such file or directory: '/usr/local/cpanel/3rdparty/mailman/lists/listname_domain.tld/config.db.last'

Workaround

To recover this file, you will want to restore these from a recent cPanel backup. In this case, the file /usr/local/cpanel/3rdparty/mailman/lists/listname_domain.tld/config.db.last needs to be restored from the backup file. 

For more on how to do this, please see the following article:
How to manually extract individual files from a cPanel backup with the tar utility

In the event that you do not have a backup to restore from, you will want to move the list data aside and re-create the mailing list. 

1. Move the list data aside:

   mv -v  /usr/local/cpanel/3rdparty/mailman/lists/listname_domain.tld{,.$(date +%s)}

2. Re-create the mailing list within cPanel
3. Verify that no lists report any errors with the following command:

   /usr/local/cpanel/3rdparty/mailman/bin/list_lists