When in cruise on B787 the aircraft begins to deviate off course slightly then progressively gets worse in VFR and IFR day/night any situation, until a high speed spin develops and then kaboom!!!. Overiding merely disengages the AP. Tried to correct back on course, disengage/re-engage auto pilot, reduced speed, reduced FL absolutely nothing works. Very annoying and needs to be prioritised as a fix in next update please.