Corrective blendshapes import problem

I am trying to import a rig with quite a lot of blendshapes done in SHAPES Evaluation plugin, not with the Maya Blendshapes feature. I can see all the blendshapes in the Shape Editor exactly as I would see them if I had created them with the Maya Blendshapes. I have exported the rig as FBX with the blendshapes checkbox selected and imported it to UE4 with the morph targets checkbox selected.
however, the importing process stops at 80% and UE4 is stuck from then on, can’t do anything but end task. It happens each and every time I try to import the rig.