Stress or resting. That's all I understand it to be.
I would have left it alone until I know the entire root is gone. Sometimes cutting that portion makes it worse. Sometimes that root with the shriveled tip will grow a new tip from the shriveled end. Or it will grow a new tip from the sides of the roots. You'll start noticing a bump on the root and a new node forming by it splitting open the surface of the root enough for a new one to come out.