Why do you say that? Does the error gone when you deactivate the WPML plugin?
If you're using a child theme, try switching to the parent theme to see if that makes a difference. The conflict could be in your child theme customizations.
Enable WP_DEBUG and WP_DEBUG_LOG. You might be able to see an error message on the site right away. If not, the error log could reveal where the problem is originating.
If nothing works, please provide us the site URL and login credentials on a "secure note" so we can take a closer look.