Comment (by Erik Schnetter):

The original intent is that ni is the outward normal of the physical boundary, and zero in the interior. For example, ni=(-1,0,0)` at the lower x boundary, and ni=(0,1,1) at the upper y-z-edge. This direction is needed for some boundary conditions, e.g. for the standard BSSN radiative boundary (which doesn’t use LoopControl).

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2385/incorrect-normal-vector-when-looping-over