system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do Webpages on mobile devices especially still jump around frequently while loading? It goes as far as you cannot reliably trust what you about to hit will be still there when hitting it. Can't there be a load order that prevents that?
gpt
Scripts load at various times, often triggered by other scripts and elements on the page. Also, many images are not properly coded with width/height info causing the image load to make the page fluctuate.

A fun way to learn about how the web really works is to use an add-on like noscript. You will have the base page load (html) and each script in the page will need you to manually turn them on one-by-one. Well, you don't HAVE to, there is an "allow all scripts on the page" button.

Some pages only have one or two script approvals required. Journalism/media sites will have so many you will need to approve them all, then approve the scripts those scripts loaded. Possibly multiple times.

As the scripts load, you can watch the content on the page jump around as they load in. That's what is happening normally every time you load that page, just mostly all at once.