1.- I suspect this might be just a false positive and the warning message just got stuck in the backend. For this reason I would like to ask you to follow this steps:
- Create a full copy of the site before making any change.
- Update all outdated plugins and themes.
- Flush any cache memory that might exists.
- Go to WPML -> Support -> Troubleshooting link -> Apply the troubleshooting steps highlighted in the attached image.
If the issue persists then connect to the database, look for the table that ends in '_options' -> Search and delete this message.