My 90 is my fourth Sako and first £3k rifle and I'm not impressed after exactly the issue you describe. Just five stalks after initial zero and load development and I went back to Corinium for my monthly range slot to check zero and practice, to find the rifle was shooting an inch low and left. After re-zeroing and continuing to practice, groups were inexplicably widening even further. Paul and I were both scratching our heads until he checked and re-torqued the stock screws. Problem solved! Apparently, Sako's are infamous for this problem although Paul has said it should hopefully not re-occur now the screws have been properly torqued. I sincerely hope so but am also quite shocked to encounter with the most expensive of my four Sako rifles to date.