1st Reason: The butt plate is too down.
Solution: Move the but plate up. Always move it 1-2 mm only and step by step you will reach the correct adjusting.
2nd Reason: Cheek pressure was less as usual.
Solution: Check contact of your cheek on the cheekpiece.
3rd Reason: The gunstock is too long.
Solution: Decrease the length of the stock step by step 1-2 mm.
4th Reason: The right shoulder was not enough relaxed towards the down.
Solution: Relax right shoulder a little bit more down as by last shot.
5th Reason: Left shoulder was too much down.
Solution: Relax left shoulder but don't push it too much.