Cloth Simulation runs terribly after upgrading

After upgrading from 5.0.3 to 5.1, when my character’s cloaks enter LOD0 range, my fps goes straight down to 8. (edited this because it said “0”. it may as well be zero as it becomes a slideshow, but it consistently says 8 fps. i feel like there’s a physics timer off somewhere)
It does this in the skeletal mesh for the cloak as well. If I turn off the cloth simulation the problem goes away.
Any ideas what could have caused this from the upgrade?