Error when trying to register a new membership

After many CB updates a couple of days ago, new members cannot register. After filling out the basic application form the user is taken to the registration successful page, but there is an error message at the top of the page: Duplicate entry 'w0' for key 'y2vfp_users.idx_username'
(y2vfp is the database prefix)
And the email confirmation message is not sent to the user

Looking at the Joomla users database, it appears that since CB plugin updates, the system generated usernames, done with CB Auto Action by adding a "w" to the user id is no longer working. The usernames showing in the Joomla users database are now the user's email address. And in Comprofiler database, cb_username is w0 and then subsequent new registrations show cb_username as NULL

Community Builder 2.11.0+build.2026.07.31.14.26.35.e46e38af0
CBSubs 4.9.0+build.2026.07.16.20.06.54.da02532e5
Joomla ‎4.4.14

The following had a regression bug on Joomla 4. Either could be causing a fatal error and potentially breaking subsequent processes. New stable releases have been made yesterday for all 3. Please update them if installed and see if that resolves your issue.

CB Content Bot
CB Replacer Bot
CB Author Bot

Please however make preparations to migrate to Joomla 5. Your version of Joomla is end of life. While things may still work on Joomla 4 we no longer officially test it anymore.