Help Rope jittery with pin and fixed contraints

[ftf_shess]

Hello,

I'm seeing a lot of jitter for a rope on both ends - it has pin contraints on one end, and fixed pos/rot on the other in Unity 2018.4.8.

The pin constraints on one side are pinned to an object with a rigid body that is set to kinematic because it is moved by a player in VR.  The rope is parented under a different object with a rigid body that is also set to kinematic to be moved by the player's other hand in VR.

I've tried making sure the phases are the same and increasing the iterations of Pins, with no change.

Changing the update order to anything other than FixedUpdate makes the side with fixed constraints look correct, but it causes the side with the pinned constraints to wig out and go down through the floor for some reason.

This "down through the floor" behavior happens if I follow the pendulum tutorial online and set the update order to AfterFixedUpdate or Late, so I assume that for a pin constraint, this is just not the correct order in general.

I know this is an odd combination, but I feel like I'm missing something obvious in the setup.

Any thoughts or pointers?

Thanks!