When viewing a single child comment thread (ie viewing a response to your comment that is already a few comments deep in a thread), you are given two options at the top of the comment section, one to "view full context" of the thread you're in (expected behavior: give context up to the parent comment and show only comments in that thread) and one to "view full comment section".
As of now, at least for me, both options simply give me one additional parent comment above what I can already see (in my previous example, it would show the comment I originally replied to). To get to the full comment section, I have to press the option and reload the comment section over and over until I get to the parent comment, at which point "view full comment section" actually does what it says.
As the other commenter said, it never works the intended way for me. I want to say that it used to work and an update broke it but I can't be 100% sure.
I suspect it has something to do with how it tracks the origin. Like when you click into a reply it seems to be thinking the original reply is the root of the post.