Before this ticket is assigned to one of my colleagues I will give the initial answer.
The screenshot shows a warning which is not a PHP error and whatever process there is should work ok.
Also, the warning does not seem to have originated from WPML by checking the file which the warning originated.
I suggest that you do the initial test below:
- IMPORTANT STEP! Create a backup of your website. Or better approach will be to test this on a copy/staging version of the website to avoid any disruption of a live website.
- Switch to the default theme such as "TwentyTwenty" by going to "WordPress Dashboard > Appearance > themes".
- Go to "WordPress Dashboard > Plugins" and deactivate all plugins except WPML and its add-ons.
- Check if you can still recreate the issue.
- If not, re-activate your plugins one by one and check the issue each time to find out the plugin that causes the problem.