Check your deadzones, the MSFS autopilot logics differ from real life. If you would accidentally apply some force with autopilot engaged in real life nothing will happen as you can’t physically move the controls with the autopilot engaged (until exerting enough force to trip the autopilot offline).
The MSFS autopilot however can be overruled easily, the slightest control input, for example a joystick not 100% centered could throw it off. Just turn the autopilot ON and move the ailerons and see what happens! Its comical, the aircraft follows your input but the autopilot steers the yoke in the opposite direction 
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