usually, when you reply to a post (rather than the whole thread), the replied to post will get a collapsible UI element that shows the replies right under the post:
In addition to that, the response post shows an indicator that this post is a reply to another post and links back to it:
For some reason, both of this has disappeared from my own forum. Does this only trigger under specific circumstances? Or should it be visible all the time? Or did I turn off some setting?