Redux error

Hello,
A client reported a problem with a plugin in the backoffice. His problem is, the results of a search do not appear when he types the 3 first letters of a product (message shows : “The results could not be loaded”).
After inspection of the error logs on our server, I spotted this error that seems to indicate a problem with Redux :

AH01071: Got error 'PHP message: PHP Fatal error: Uncaught TypeError: Return value of Redux_Options_Constructor::default_values() must be of the type array, string returned in /home/xxxxxx/public_html/wp-content/plugins/redux-framework/redux-core/inc/classes/class-redux-options-constructor.php:699\nStack trace:\n#0 /home/xxxxxx/public_html/wp-content/plugins/redux-framework/redux-core/framework.php(573): Redux_Options_Constructor->default_values()\n#1 /home/xxxxxx/public_html/wp-content/plugins/redux-framework/redux-core/inc/classes/class-redux-options-constructor.php(269): ReduxFramework->_default_values()\n#2 /home/xxxxxx/public_html/wp-includes/class-wp-hook.php(303): Redux_Options_Constructor->register()\n#3 /home/xxxxxx/public_html/wp-includes/class-wp-hook.php(327): WP_Hook->apply_filters()\n#4 /home/xxxxxx/public_html/wp-includes/plugin.php(470): WP_Hook->do_action()\n#5 /home/xxxxxx/public_html/wp-admin/admin-ajax.php(45): do_action()\n#6 {main}\n thrown in /home/xxxxxx/public_html/wp-content/plugins/redux-f...', referer: https://www.xxxxxx.xx/wp-admin/admin.php?page=woocommerce_pdf_catalog_options_options

Is this problem due to a recent upgrade of Redux ? How can we fix this ?

Thanks for your answer.