Most likely you are just experiencing poor interaction between how we do autopilot following and the AP implementation in that aircraft. Most aircraft are fine, but some just don't like it.
This is with the default XP12 Baron? I'll see if I can reproduce.
The usual issue is that we react to the elevator/aileron servo telemetry and move the stick accordingly, but the sim has no idea that you the user is not pushing on the stick. So if the AP moves the servo forward and we react, this adds down elevator to the axis, which the AP then tries to correct with aft movement of the servo, we react.. round and round in circles we go.
Its one of the big issues with trying to do FFB outside of the sim when the sim has no idea whats going on.
