I've had this problem a lot and never found a fix. I googled it again and the OP in this post on the UE forum says the solution is to "retarget the animation to a different skeleton/mesh and then retarget it back to metahuman." I haven't had a chance to test it yet.
https://forums.unrealengine.com/t/stretching-glitch-on-metahuman-hands-after-baking-animation/2023269

0

Thanks, I'll try that! My animation works fine in the editor, but the issue happens only when I export it

I had this issue before, and the problem was that I baked my animation with the FK CR. Baking the animation with the MH CR fixed it. You might wonder why I used FK CR instead of the MH control rig, it's because I was trying to get a perfect A pose from an empty frame. Baking it with MH CR gives some random rotations while transitioning to my animation, and FK CR worked better for me until that issue. After browsing here, I found that Bassline has posted an A pose that can be used. I hope Reallusion team includes some good poses with the Metahuman Live Link Kit!

@Bassline303 boss I still cant put the animation on imported fbx file from iclone without auto setup for the spring effect, it distorts the limbs when applying animations. Is there any video demo on your unlisted section regarding this ?

UE5.5 final is out !