Single regenerated chunk

I've just noticed that a single chunk in my world appears to have regenerated. I am certain that this has happened very recently and I have confirmed this by looking at a backup of my world from a couple of days ago. The backup from a couple of days ago shows a complete wall and my current save shows the same wall with the regenerated chunk in the middle. Images are attached. My world seed is 6440625432857030074 and the chunk in question is chunkx = -74 chunkz = 17