Hey there, Just exact the animation, install blender’s beta, install my addon for it, bring in the animation/follow video tutorial, and get a file you can re-import straight up without any of the head-hake.
I guarantee it will fix all your problems.
Unreal forum thread.
https://forums.unrealengine.com/development-discussion/animation/1621362-bonebreaker-free-blender-plugin-for-mannequin-animation
Website w/ download
Instructional video on how-to
and a latest blender link
Make sure to get the 2.8 beta.