nice find!
I can see your comment reply in my inbox and vote on it, but it's not here at all.
polsaker fixed it - the deleted comment still collapses, but you can now expand it to see the children comments
It's applying the 'hidden' tag to the pchild child comment block, which hides them all - https://i.imgur.com/wTCuWwH.png
I get off work in a little bit and will get on this
Fixed. Next time please report bugs here.