Resolved
Overview of the issue
For sites hosted on WPEngine, some WPML actions, including logic for synchronizing meta field value, can fail.
This is caused because WPEngine limits MySQL query length to 16K, according to their manual
Workaround
It is possible to turn off this limitation set by WPEngine by adding the following to your site’s wp-config.php file: define( 'WPE_GOVERNOR', false );