The experimental Offset Root Bone node does not respect velocities, meaning that it does not work when a character is based on a moving platform. The capsule will rotate with the platform, but the root does not.
This was fixed in the Foot Placement node using Reconstruct World Plant from Velocity. Implementing a version of this for Offset Root Bone node could fix the issue there, as well.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-305539 in the post.