IK bones stretching vertices to ground during animation (UE4, 3DS Max, using default skeleton)

I modified the 3rd person example skeletal mesh to a simplistic model in 3DS Max 2016 student edition, by deleting all but one faces and building thereon, thus leaving the hierarchy just as it is needed to re-import to UE4 without any changes and without touching the skin modifier.

In Unreal, the problem appears upon animation, where a vertex from each hand, and one from each foot, is stretched to the ground, and in Persona I see that it's the ik_hand_l and ik_hand_gun bones, as well as the two IKs of the feet, though due to overlapping names I can't make out the entire bone name.

Another issue I successfully dealt with was the model flickering, as suggested I deleted the physics asset and that was corrected, it seems to be a frequent problem so I don't think it's particularly related.

Here is the related post in the Unreal Engine forums with an image of the problem.