Unless you "inhaled" something that went through the SC - they don't "get loose"
The most common issue is a bad boost gauge
The second most common issue is bad Bypass valve that is not closing - The Bypass is SUPER critical on Twin screw .. if it hangs closed on idle you will literally FRY the SC, Then best practice I tell everyone I do an SC for is to always look at the bypass to make sure its open at start. Since it run off engine vacuum you should make sure the line to it is good - if its hanging open the boost is possibly leaking - if you actually closes on start up the diaphragm is probably good - but you should acheck all that periodically. Its also good to have the boost line separate from the bypass vacuum sense - that should be dedicated.
Third most common is a slipping belt - Belts age, stretch and come loose. Whipples are not very efficient - they take more HP than any other SC to turn, the 4,0 takes well over 100HP even at mild boost, so it hard on the belts, especially if you are on and off the gas alot. Best practice change belts every season and check tension 2x a year. If anything was bad like an idler of tensioner the SC would throw the belt - thats the only reason other than alignment (which never changes) that it will throw a belt
I am assuming you don't have an ECU that does data logging or lets you read the MAP sensor.
The MAP will tell your the "real" boost and a data log will tell you everything else such as slipping belt or slow bypss etc.
Lastly a Boost leak is a pretty typical cause of low boost - so any line on the Pressure side of the manifold, or anything loose on the bypass. If you had a bad gasket or something like that the idle would be noticeably bad.
Of course anything mechanical in the engine will cause that too - leaky valves, flat cam etc. But you would likely notice bad idle, hard starting (un even when it cranks - hard to describe) and general bad operation ...
Its likely 1,2,or 3
