Call to a member function load_shortcodes() on null

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I reinstalled Unyson and manually installed the required extensions in the child theme:

• backups
• builder
• forms
• mailer
• megamenu
• page-builder
• portfolio
• shortcodes

I now get this error on the front end:

Fatal error: Uncaught Error: Call to a member function load_shortcodes() on null in /public_html/wp-content/themes/jevelin-child/framework-customizations/extensions/page-builder/class-fw-extension-page-builder.php:145 Stack trace: #0 /public_html/wp-includes/class-wp-hook.php(324): FW_Extension_Page_Builder->_admin_filter_fw_post_options(Array, 'page')

This issue is similar, but the error contains "non-object" instead of "null", the issue is closed, and no solution is provided on that thread. If I activate Twenty Nineteen with the same extensions, the error persists. Any pointers are appreciated.