How can you use a 4-axis or even a 3-axis autopilot approaching and landing on a moving ship with no instrument approach aid?
FED - it depends on what their SOP is for the circuit - it could well be to engage ALT hold (which will be in the cyclic channel on 3 axis) so, if you are not used to managing the AP and you lower the lever to start your descent without disengaging the ALT, the AP will bring the nose up to try and maintain height and reduce your airspeed.
The Sumburgh crash was an exercise in poor use of AP as well as poor CRM so it's not too far fetched to suggest it could have been a factor here.
I have been teaching on an aircraft with 3 axis AP for the last few years and the number of students who get 'lost' in the AP (which is only doing what they asked it to do) is quite high, especially in a high-workload scenario).