Guys, hope you could helpout. Boost Issue

Hi guys, I would appreciate if anyone could enlighten me. My 07 golf GTI(DSG) has got a problem with the boost for the past 5 months. It felt like an NA car now. It used to be able to hit 1.5 bar but now it will never go past 0.5 bar no matter how hard I accelerate it. There isn’t any fault codes on VCDS. I tried reset battery and afterwards the car will be fine for maybe an hour or so till it goes back to the problem again. Sometimes I would purposely trigger a fault code on the VCDS(ex:unplugging the MAF sensor) and then clear the MAF sensor fault and the car will run fine for another hour again. Have been to few good workshops but the problem is still there.

The following is the details of my car
-APR KO4(Recently upgraded the newest version but still doesn’t work)
-APR HPFP
-THS intercooler
-BMC CDA Air Intake
-Full Miltek Exhaust System
-S3 Injectors
-IE rods
-Quaife LSD
I’m not sure if I still miss out on anything.

This problem started when I fitted my stock exhaust for inspection, right after inspection I put back the Miltek exos and the next morning this problem starts happening.

So far I’ve changed the following parts
-Updated to APR ko4 latest version
-N75 Wastegate frequency control valve
-PCV
-Brake Vacuum Pipe
-Diverter Valve
-Purge Valve
-Both Knock Sensor
-Did smoke test and have no leakage
-Wastegate actuator is fine too
-Swop MAF sensor, it doesn't work still

Thank you so much guys if you could give me some directions.