I know this is a year off but I am having a similar problem with animation. I have a custom clothing model that I created directly from a Metahuman model in Blender, which I then exported with the armature back into Unreal to attach to the Metahuman skeleton. However, despite the clothes being perfectly rigged in Blender, meaning they move perfectly with the Metahuman armature bones, when I attach the clothing to my Metahuman in Unreal using the meta’s skeletal mesh, the clothes do not animate at ALL. I cannot figure out why this is.
My only guesses were either a problem with an import/export setting, or using the wrong skeletal mesh to target, but I cannot figure out what.