No, sorry. That was my first guess, because the page didn’t contain a slider where I could have seen it. I believe you when you say that the setting was activated, it’s ok.
But the problem is that I can’t see the issue your GIF shows (without the custom CSS), nor can I replicate it. It adapts the height as soon as every image is loaded, see: CleanShot 2024-06-26 at 15.42.23 · CleanShot Cloud
There is no issue as well on my test site: - link removed -
I see you’re using phastpress - have you already tried it without phastpress and using jpgs instead of webp images? This is also just a guess, as I’m not a PhastPress user - but it’s worth a try.