Question Issues with blender shake keys (and normals?) in Unity

Hi,

I have imported an fbx from Blender to Unity 2019.2 and am getting strange artifacts that I cannot account for. My hunch is that it has to do with how Unity is handling normals for blend shapes.

Below you will see the imported fbx in a run animation, compared to the same exact blender file( same animation and same frames) fed into the unity project using a live sync (MeshSync plugin). The blender file uses shape keys to alter the midsection of the character during the run animation to keep the geometry smooth. This works well in the live sync example, but does not work whatsoever and gives artifacts in the imported fbx. I have followed suggestions on similar threads saying that fbx model import settings should have 'Legacy Blend Shape Normals' checked or alternatively having both normals and blend shape normals set to import. This did not change anything. Any thoughts about what is happening here?

Thanks!

https://giphy.com/gifs/ehSLsGELJAEC7cDcEG
https://giphy.com/gifs/52PS1k6jBOMRWOXUCd
https://giphy.com/gifs/2cFrZC8mbzLchB3KXG

compared to how it should look (live sync)

https://giphy.com/gifs/ihZQySX9s2uItUhQ2e
https://giphy.com/gifs/dxx6Z7aBw9PhOYTLgE