I equipped a full set of all 6 griffin school gear items and the achievement for doing so did not update on the GOG galaxy launcher

It finally updated later when I closed the game. The odd thing thing was the times it noted for achievements were correct for earlier. Seems it isn't reading it till log off. Maybe it is suppsoed to do that so it isn't slowing the game?

Yes, I too have noticed the achievements list is only updated after the game has been quit - it seems fairly likely this is intended rather than a bug.