I’ve asked to WPML support. They say: “page is corrupt for some reason and it is not possible to use the method theme developers meant to use”: https://wpml.org/forums/topic/i-cant-duplicate-a-page/
Unfortunately, after I few attempts I don’t know why /en-us/heromask-languages/ doesn’t seem to exist and empty /en-US/heromask-languages-2/ has been created instead.
I’ve recorded a video to show you: https://d.pr/v/Xior5D
Any idea about of to fix the corrupt page?