This is from a conversation with no replies. But despite there are no replies it gives you the last reply date. (Anonymous is a made up name if you are wondering)
I suggest changing Last Reply Date to Last Message Date. A message is not the same as a reply.
This is from a popup. Here it says Last message by. All good.
Now if you hover it you get this:
So it says Last message by and when you hover it, it says Last reply by.