When viewing a limited thread of comment's (for example, clicking on a comment from my history) There are two buttons at the top of the comments: 'Show context' (which should just show the next comment up the chain) And 'show all comments'

Both of these buttons have done exactly the same thing for the entire time I've used this app (around a year now): they both show the next comment up the chain.

You have to tap either button several times to get to the full list of comments. ie, show all comments. It doesn't matter which of the two you use, they both only show the next comment and not the full thread.