After beating the first boss, loading into the next zone, and dying, my performance continuously fell after each any every room cleared. By the end of that run, I was at around 20fps. My CPU was at ~25% usage, GPU at 10% usage, and RAM at 20% usage during this.

I would assume it's some sort of memory leak, but who knows. Restarting the game seems to fix it, but just thought i'd report it.