I notice that the topics tags are very bright in comparison to the rest of dark mode. (For instance, the Football topic has two ‘tags’: “Football” and “Sport” which are both white boxes.)
When you reply and quote a user’s post directly, you of course get the little profile image for the replied to user in the top corner. Clicking on that profile pic then expands the new post with an inset of the replied to post. In dark mode, the insets aren’t readable, because the inset box is still white, but the text has been changed to white as well.
Where daws has replied to AlexCorbin, there is now a little version of Alex’s Profile pic top right of Daws’ post, expanding that reveals a big white box with Neil Buchanan in it. However, in those boxes, text is white as well, and so, invisible.