The stock OPV (over pressure valve) is set stock to about 15 bar which is far too high and causes lots of problems trying to dial in your espresso shots.
One alternative is if your machine can achieve 9 bars in pre-infusion manual mode you can pull your entire shot that way.
You can try adjusting the stock valve which has limited adjustability. It may leak or not be able to open far enough in some cases to achieve a lower pressure. This is worth trying before replacing it.
As an alternative you can replace the valve with a brass OPV valve:
Vibiemme Bypass Valve OPV | Replaceemnt parts for Vibiemme Espresso machne - Espressocare