Some plugins use a special configuration file in order to be fully compatible with WPML. This configuration is often stored in a WPML repository and is fetched when you activate a new plugin. Sometimes, caching issues prevent this configuration from being updated automatically.
In case of caching issues, you can can run this update manually.
Go to Dashboard → Updates. Scroll down to the section called Theme and Plugins compatibility with WPML and click on the Update button.
WPML will load the most recent version of the language configuration files for your plugins.