Sometimes (possibly correlating with access via an iPhone or iPad browser, and/or a slower connection) after opening up a topic, the view will jump around (usually to an earlier message). Also, this somehow clears the browser history for the tab, so I can no longer use the “back” button.
Any topics, really. Even on this one, scrolling down from @defjaf 's post to yours changes the URL from https://discuss.python.org/t/discourse-view-of-a-topic-jumps-around/62552 to https://discuss.python.org/t/discourse-view-of-a-topic-jumps-around/62552/2. (And now, for this reply, presumably https://discuss.python.org/t/discourse-view-of-a-topic-jumps-around/62552/3.)
And, yeah, they are at least nice enough to keep those updates out of the navigation history… which I guess isn’t so nice, when there’s a bug that causes your browser to lose all navigation history as a result.