Welcome to WPML support. Is this happening only on that specific field or other fields of the page too?
I wonder if you do as follows it fixes?
- Go to your Dashboard > Pages.
- Open the edit screen of the original page. You should see a pencil/circle/gear icon in the sidebar options under the "Languages" section.
- Make a small change, for example, add an extra blank space at the end of a sentence/paragraph.
- Save it.
- You should now see that a circular arrow appears beside the 2nd languages links, this means that an update is required.
- Edit the translation again and save it up to 100% translated.
If the issue persists, I'd appreciate it if you could give me the URL/User/Pass of your WordPress dashboard after you make sure that you have a backup of your website.
It is absolutely important that you give us a guarantee that you have a backup so if something happens you will have a point of restore.