Before this ticket gets assigned to my colleagues, I will try to help.
The proper way to translate strings depends a lot on how they have been implemented inside the theme/plugin.
In our case, those strings might be admin-text strings, so method 2 will probably resolve the issue for us and make those strings start showing up in WPML > String Translation. However, please try both methods and see if one of them resolves the issue.
Method 1:
Go to WPML > String Translation and at the bottom of the page you will find a checkbox called "Look for strings while pages are rendered". You can enable (check) that and then go to the front end to a page where you have that string showing up and then go back to WPML > String Translation and search for that string and see if it now shows up.
Method 2: If you can't find them inside the WPML > String Translation, they might be added as admin text strings.
