That was a bug? I remember overusing that during the rooftop mobs lol.
I was playing with Low settings at 1080p the whole time (High was unplayable). It was actually running pretty good up until the last stretch before the boss. I think it was so many otomos and big crystals visible in a straight line. It affected the boss fight quite a bit too. It was still pretty playable, but definitely slower than the rest of the game up to that point. So I think just general instancing optimizations or LOD issue. No big deal really, my 'work' computer really isn't very strong for gaming.