Can't update cPanel due to failed or aborted transfers

Symptoms

If an account transfer fails to complete or you abort it, you cannot update cPanel, and this message displays on the cPanel & WHM Upgrade Blockers page in WHM:

There are active transfers to this server. The system will block updates until those transfers end, or a user aborts them. Please read our Transfer Tool documentation for more information.

Description

When the system detects unfinished transfers, it does not allow cPanel updates to proceed.

Workaround

1. Identify the unfinished transfer's session ID:

   -bash-4.2# sqlite3 /var/cpanel/transfer_sessions/whmxfer.sqlite "select sessionid from sessions where state != '100'"
   cpthisisatestcopya202007210601035ab

2. Remove the session ID from the transfers database:

   -bash-4.2# sqlite3 /var/cpanel/transfer_sessions/whmxfer.sqlite "delete from sessions where sessionid = 'cpthisisatestcopya202007210601035ab';"

3. Move aside the update-blocker file:

   -bash-4.2# mv -v /var/cpanel/update_blocks.config /var/cpanel/update_blocks.config.bak