We are not reading all the key flags and we do not import correctly start key and end key tangent.
I create a shelve but this is not the complete fix, we must do this only if we do not have fbx ket flag eTangentGenericClampProgressive.
We also have to create many different test and make sure we follow the fbx flags and get the same result
see fbx sdk documentation
Import the attach fbx
Make sure you import animation and also custom attribute animation
open the the imported animation "CurveTwoKey_Anim"
The tangent of the first key and the last key are horizontal, it should not compare to what we got when we import it in Maya.
There's no existing public thread on this issue, so head over to AnswerHub just mention UE-98071 in the post.