BeBuilder is based on Custom Fields and allows to create content using included blocks, items and much more. If you faced an issue that content made with builder does not save, no matter what, you have to create phpinfo.php page and check if the following limits are correct:
If you are using the Wordfance plugin, it is likely causing this issue.
Go to the Wordfance firewall settings, activate learning mode, open the page with this problem, update it, and activate Protection again. These steps are also described here:
https://wordpress.org/support/topic/admin-ajax-php-file-blocked/#post-13508663Thanks to that, Wordfance will learn which actions are safe and stop blocking page updates.