Gulli
Interesting that we're now 3 weeks past the event, and with 15 pages of posts on this thread we are still totally under speculation mode. The August 2015 accident after about this same period of elapsed time they were pretty sure what caused it and the Emergency AD was going out.
II had the reason for the ditching in post #196. Investigators are looking for the possibility of a possible chafed wire which may have caused the Autopilot issue.
According to information, the same autopilot issue was evident outbound but the crew landed on the rig without a problem and attempted to troubleshoot Then after departure when the issue came up again decided to ditch.