FPS Slowdown Concerning Boulder

[Thaliur]

This was the place where it happened to me, and TheCollective's description sounds like it was that place for him, too, I'd say.

I just realised that the puddle was not on fire when I moved the boulder on my first play-through, when it was smooth, and was on fire on my second play-through when I had this framerate drop occuring.
This led me to a new hypothesis

It could be connected to lighting and the way shadows are created.
When the boulder approaches the flames, it casts a shadow on the wall behind it. then, as it touches the fire, the light source moves inside the boulder. So the algorithm that tracks the object silhouettes could get stuck finding a way out of the boulder.