Only worked in 3ds max for a short time and never done animation in it, I do animating through maya atm. But i was having this problem when i tried to import a animation into UE4 from maya.
I fixed it by baking the animation to the skeleton of my model before exporting just the skeleton as an fbx.
Then i re-imported it into maya on an earlier version of the rigged model with no key-frames on it.
From there i selected the skeleton and the model/mesh and exported them together as an fbx re-imported them into UE4 and the animation worked fine.
Hope that can help.