If the autopilot is compass based I imagine it would be gyro compass, not a magnetic compass.
There a couple of posts on ForArgyll that appear to be by members of the crew, clearly suggesting fatigue as the probably cause.
June 16, 2013 at 8:47 pm
Hey it is seamans life, true is…: 7 crew on board, completed loading at evening + securing of cargo, lashing + unmooring, All mooring unmooring and Navigation without Pilot, Coran point Loch etc.. All pushing Agent+ charters,receivers etc… as i know on this tipe of vessels all crew involved in securing of cargo, so 2nd mate and ch. mate also tired, 2nd mate go at watch at 24 and 100% tired … Continious soon.