Advanced Custom Fields - Uncaught TypeError: array_keys(): Argument #1 ($array) must be of type array...

Overview of the issue

You may encounter a fatal error when attempting to update Advanced Custom Fields repeater fields if the translation is a duplicate in environments running PHP 8.1 or higher.

PHP Fatal error:  Uncaught TypeError: array_keys(): Argument #1 ($array) must be of type array, null given in .../wp-content/plugins/acfml/classes/class-wpml-acf-repeater-shuffle.php:175

Workaround

Please, make sure of having a full site backup of your site before proceeding.

• Open …/wp-content/plugins/acfml/classes/class-wpml-acf-repeater-shuffle.php file.
• Look for line 24.
• Replace:

  	private $meta_data_after_move;
  

• With:

  	private $meta_data_after_move = [];