SIN and COS tend to be a resolver type of angle “encoding”. A very robust passive type of design. You need an excitation AC signal and you get two AC signals back, one with the SIN of your angle and the other with the COS of your angle signal. Typical those signals are differential and isolated from GND, because they come out of a transformer style winding. That makes them robust against noise on the harness. A possible scenario, where you might get wrong or offset values if there is a short between harness lines either the output or the excitation line which is not detected. That might tell us, why exchanging the sensor did not improve the problem.
For Boeing it should be easy to make some tests on the ground to determine what harness failure can create a 22 degree error in their “normal” flight orientation.