For at least a year, Twitter links have only loaded the one message, not any other messages in the thread, or other irrelevant tweets like it used to. Happens across browsers, with configurations that aren’t particularly exotic. No idea what’s going on.
This is, from what I understand, intended behavior. The worst is when people link the final tweet in a thread so you just get the last message and see no other context. For me, I don't see the value in people posting twitter links.
It’s certainly not how it used to work, or a behaviour that makes any sense. And I’m pretty sure it was behaving this way even when I was logged in (before I finally deleted my ancient account that I hadn’t used for five years).