I solved this problem myself.
in /plugins/advanced-custom-fields/core/fields/_functions.php Line: 330
change maybe_unserialize() to unserialize()
before:
$field = maybe_unserialize( $field );
$field = maybe_unserialize( $field ); // run again for WPML
now:
$field = unserialize( $field );
$field = maybe_unserialize( $field ); // run again for WPML