Background of the issue:
I am working on a site under development and updated translations when suddenly WPML started giving critical errors. I have done basic troubleshooting steps like updating plugins, deactivating and activating the plugin, and deleting ghost posts and cache.
Symptoms:
Error: Uncaught InvalidArgumentException: item should be a Collection or an array or an object in /data05/virt41565/domeenid/www.rameedia.eu/htdocs/ruumala.com/wp-content/plugins/sitepress-multilingual-cms/vendor/wpml/fp/core/Obj.php:112