It happens here all the time with half of the threads.
The twitter iframes don't have a min-height or something like this. They load as one-liner links and later expand to whatever they need.
For example this post #1,740 :
Trump era: Fascist dawn, or road to liberation?
That's the problem: they aren't IFRAMEs. They're a bit of HTML (BLOCKQUOTE usually) and then some JavaScript.
The JavaScript runs, sees the specific blockquotes already rendered on the page, and dynamically turns them into an embedded tweet - which changes the height of the page's content
This is the "new" way of doing embeds, and it's very dumb. Embeds like those from YT don't have that problem because they're IFRAMEs with a set width/height.
On top of that, Twitter embeds are generally pokey when loading.
On SOTT, tweets are wrapped in IFRAMEs and then there is some JS in both the wrapper IFRAME and in our editor that talk to each other. Once the tweet is fully rendered, the JS in the IFRAME talks to the JS in the editor and resizes/adjusts things so that everything works properly.
The other way of fixing it would be for XenForo's JS to hold off on jumping you down the page, but that's not terribly reliable as I discovered with SOTT - mostly because Twitter's rendering of embedded tweets is horribly unreliable and buggy.
So in short, any embeds like tweets that use this method are going to cause problems. Not much to do about it except hope that XenForo fixes it at some point...