Animation Rigging 2019.2 -Two-Bone IK not reaching nearby target with all Weights at 1

First, thank you for such an improved animation rigging system! It's modularity and multi-thread nature are absolutely fantastic. Thank you for making it a regular part of the Unity engine.

Here is the situation I'm working with currently.

I have an animated character grabbing another animated prop (Boat handle). We are trying to maintain a solid contact. Without an IK solution the keyframe reduction creates "swim-y" animation with a lot of issues.

I've created a Two-Bone IK on the LeftArm in an attempt to anchor the hand-to-boat contact. The LeftArm_IKTarget is within the character rig. There is a standard Parenting component on the LeftArm_IKTarget that refers to a target Game Object within the Boat rig.

The constraints function as expected, turning of and on with the weight floats - except the arm joints start to drift away from the LeftArm_IKTarget even though the IK Box Effector continues to align with the cube on the boat handle.

What might be the reasons that the IK joints would wander away from their target?

 

Thanks Simon for the eyes on the issue. I rebuilt the constraints with only Anim Rigging components. Here is the result.
The position of joint doesn't match the IK target effector, and the IK target effector doesn't match the multi-parent constraint target. Hmmm.
The component set-up is as follows (this is the GameObject paused while running it in Editor).

And here's the Heirarchy view.


Any thoughts on the update?

 

Using the generic Parent component solidly connected the effector IKArmTarget object to the separate BoatTarget game object. The effector's position and rotation stayed together, but only the joints strayed.

Using the Multi-Parent component BELOW the Two Bone component, did not produce a clean result.

Placing the Multi-Parent component ABOVE the Two Bone component, allowed it to function properly, but both the effector and the joints strayed.