I managed to fix this.

The issue is that I need to put the coordinates in the correct order.

I have,

x' = z

y' = x

z' = y

That means, if my grid is now defined in the new system,

xold = ynew

yold = znew

zold = xnew

Therefore, while doing the interpolation call, I have to send coords in y,z,x order to get the correct results.