Some while back and to this day there are some posts in forums asking about corrective morph exports from Max to UE.
There was a thread a while back where we tried to remedy the problem but that didn’t work. Max uses Skin morph as an extra modifier to do additive morphs for correctives internally so this doesn’t work with UE.
Currently to our knowledge there exists no possible way to get the additive morph information form skinmorph and translate that to the regular morpher modifier in order for the corrective to work and Unreal to read it and no currently available scripts to do this for you, and since writing one would take a while, we found the solution to be outside Max and inside good old Blender. So we ended up with the following:
1 - In Max create base skinning on the object that requires corrective shapes.
2 - animate multiple extreme poses.
3 - export the object plus animation as FBX into Blender.
4 - create corrective morph targets (Tutorial youtube).
5 - Export FBX back into max extract the morph target and apply it onto your original mesh morpher as a corrective target.
With the corrective correctly working inside the morpher, Unreal should be able to read it.
Hope this helps people out.