You’ll have to have ftp access or cPanel file manager access to do.

1. Find the path of the redux/inc/class.redux_filesystem.php
2. Edit it.
3. Insert a New Line before 29 and save.

   Line 28         public function __construct() {
   New Line           $this->parent = (object)array();
   Line 29      $this->parent->admin_notices[] = array(

Referenced: https://www.wordpresshosting.solutions/index.php/how-to-fix-redux-core-inc-class-redux_filesystem-php-on-line-29/