Why does my model look like this on import to ue4?

So I boxed out this character and rigged him up using the mannequin’s rig from ue4. Then I imported him and selected the mannequin’s skeleton so it would share animations.

Now, when I swap out the mannequin with the model he can run around but his right arm and both hands specifically are destroyed.

Can someone lead me in the right direction to fix this?

Does the character has the same “A Pose”.

Maybe you need to first import the character and set a “Preview Pose”, prior to retargeting the mesh to the UE mannequin.