No, WPML doesn’t require that. All the element/post/page settings are supposed to stay the same, and other than this particular case, that is exactly what happens throughout my site.
It’s very odd.
I’ve inspected the page and I note that the code is different but I can’t understand why.
On my English language page, it is:
<div class="page-hero hide-on-mobile full-height" style="background-position-y: 0px;">
But on my Chinese-language page it is:
<div class="page-hero hide-on-mobile">
It’s using exactly the same element, so I don’t understand why the height and style are being removed.