Alembic Blender/UE4 problems

Hey guys

ok been testing with some Alembic exports from Blender to UE4 and they have been generally successful. Cloth, physics etc all export across fine but yesterday did an animation of a guy getting his arm sliced so I had the arm separate and animated it twisting and flying up in the air then keyframed physics to take over so it’s falls to the floor realistically and looks great.
But this export crashes UE4???
anyone any experience of using Alembic with UE4 please? I have watched a few tutorials and followed the settings exactly but is there anything I need to do re the export settings, I export the file same as the above ones, they imported in UE4 fine and this one doesn’t work?

any ideas please people?