Do you have to cycle the ignition to return boost or does it happen all the time?
Eg. If it is going into limp mode to protect the engine from overboost, cycling the ignition will normally resolve the issue until it happens again.
This will normally result in a fault being logged.
If it is always lacking boost, regardless of cycling the ignition, check for loose or split boost hoses, loose boost hoses Connections, seals clips etc.
You can normally hear them if this is the case.
Jas