Hi, maybe what happened to me could help you.
After Japan upgrade and UK upgrade some keyboard commands were restored , those i had deleted after the first installation of FS.
For example, the commands that control surfaces of the plane.
I recommend that you disable (in Option/Commands/Keyboard) any keyboard commands that affect the numeric keypad, especially the 8, 4, 6, and 2 keys.
After clearing these commands (ailerons, rudder etc.) the autopilot works normally.
In fact, if it is true that a movement of the joystick automatically deactivates the autopilot, even a very short press of key 4, for example, causes the aircraft to tilt to the left WITHOUT the autopilot deactivating. The aircraft will continue to turn to the left until it reaches a bank angle which will cause the aircraft to stall and give you the impression that it is a defect in the autopilot.
Tell me if this works…and excuse my bad english.
Stefano