the report reveals is that the long history ( as recorded in the dodgy dossier of unapproved e mails) of autopilot function and indication issues is what did for the guys.
I will not speculate , but feel I can comment.
When engaging an autopilot, it is prudent to ensure that the correct mode is activated and then monitor the aircrafts flight path to ensure that the aeroplane is being flown as you intended, in otherwords you watch the attitude and performance. This is even more important when single crew or , as suggested, there is a question of reliability of the autopilot. Then if it is not following the intended flight path hand fly the aeroplane.
Unfortunately we may never know what actually happened that led to the crash.