Steps to reproduce:
Go to the iClone and make sure you turned on the Spring effect for your character.
Apply any animation to your character (e.g dancing so the effect will be noticeable).
Export your animation as a MotionPlus file using the "Collect clip" feature in the animation window.
Go to the CC3 Pipeline, open your character, and press the export.
Pick Unreal Engine preset and "motion only" if you already have your character in UE4 or "mesh and motion" if you don't. Scroll a little below and select the MotionPlus file you prepared before. Also, I specified 60 fps, but I don't think it is matters.
Go to the UE4 4.26, drag & drop your FBX file to any folder.
Wait till export finishes, and open the newly created animation sequence file.


Actual result:
There is no spring effect on your character in UE4. Although I noticed it works well with LiveLink.