Starfall Crater - Extreme Lag Spikes When Black Knight Performs an Attack for the First Time

I fought the Black Knight for the first time yesterday. It was an interesting fight, but I suffered extreme lag spikes (sometimes 2+ seconds) at times. These seemed to occur only whenever he used a new attack for the first time. The first phases and the first few phase transitions were terrible, but by the final few phases the lag spikes were nonexistent and the game played almost perfectly smoothly.

I suspect that some sort of preloading of assets failed to occur when entering the Starfall Crater zone, or perhaps that some shader computations took egregiously long to perform on my computer. I don't know computer graphics, so I can only speculate.

My computer has an i7 2.8 GHz Intel CPU, and its GPU is an NVIDIA GeForce GTX 1060.