The tangent of the blendshape curve seam to have the wrong scale (but correct direction) from this UDN.
We have to investigate if 4.27 have the same issue and fix it if its the case
Create some blendshape in maya and animate the weights with a curve.
Import that curve into Unreal
Look if the tangent have the same direction and scale.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-130597 in the post.