Threaded replies or nested replies not working

I have this blog Candid Opinions where previously when one left a comment on any of my posts, my replies to him/her were nested or threaded just below their comment. But for some reason (which I am unable to detect), the replies are currently no more nested down as they used to previously. As a result, the comment section looks really long. And this happened all of a sudden out of nowhere.
For instance, this –
When I click the reply button below someone’s comment, the comment box doesn’t open up like it used to previously.

Can someone help me out?
Thanks in advance.