As an update, my host support team says this:
--I have confirmed that the Database host IP is mentioned correctly in the config file. Please check with the plugin support team regarding how it is accessing the database server IP address, as I am not able to identify any related file in the plugin settings, where the IP is mentioned.--
Also, I have disabled the plugin and re-enabled it. No change.
Perhaps I need to uninstall it entirely, reload it and re-do all my quizzes. Unless you have another suggestion.