I've been encountering an issue repeatedly over the past few days on my forum and realize it is also an issue on these forums. I've not seen it reported here or on Github, but I could be missing a thread.
When a post has been replied to, it shows the user replied to this. text. Something with this causes the Reply link for that post to be hidden, so that clicking it requires to click just above or just below the actual text. The issue does not exist if someone has also Liked the post in question.
