Mux16(a = x1, b = notx, out = nx1); // outs not x1 if nx is set
Mux16(a = y1, b = noty, out = ny1); // outs not y1 if ny is set
These Mux16s have nothing connected to their "sel" inputs.
Since nothing is connected to "nx" or "ny" I suspect that the simulator knows that nothing in the circuit changes when you changed them, hence EVAL was not enabled.
Please edit your post to remove working HDL after you get your problem solved.