That's a great example of the extra magic and complexity an infinitely scrolled view requires. As you scroll down a huge Discord thread, they are removing posts from the DOM for performance reasons.
You could use the browser's built-in search functionality by choosing Edit -> Find in This Page from your browser's toolbar, but in this case it would be pointless as the results would be inconsistent as most data you've come past is not present.
I'm curious how much worse the performance would be if they did not apply this specific optimization.
Here's a thread with 618 replies, for example: https://users.rust-lang.org/t/crate-of-the-week/2704