I just encountered this today, sometimes the car will not boost past 3psi randomly. I can keep driving and later on it will boost no problem, then a minute later it won't boost past 3 again. It's not the gauge malfunctioning, there is a noticable loss of power.

Any ideas? This is my first supercharged car, could it be the bypass valve?

 

Possibly useful that I just remembered, this week I have been getting a message on the screen telling me to check the gas cap. It did not come up when I was experiencing the loss of boost though.