** Update **
the issue was caused due to faulty spark plug leads causing weak spark and misfire under load. now i have more experience with misfire and bogging issues i can say, check your ignition system condition first as it seems ignition breakup is the most common cause of this fault.

Hi all,
I have an aus spec. ‘99 wrx stock apart from A’pexi intake, cat back exhaust, TMIC and blitz dual SBC. 20,000km ago replaced a faulty maf, new NGK ird plugs, new coil, new 02 sensor and replaced the vacuum lines. I have set the peak boost around 100kpa/~14 psi. after a bit i’ve searching i’ve found nothing similar, so…

my WRX has developed an issue where no matter what throttle position or RPM the engine is at, as soon as around 0.6 to 0.7 Bar / 10psi boost is reached the engine bogs and looses all power completely, as if it’s running lean IMO. i’ve also found that this issue is particularly bad in the first 10 - 15 minutes of driving and when the fuel tank is around 1/4 or less, although it’s a constant issue. My thoughts are maybe a bad fuel pump, or perhaps bad FPR (like a fuel starvation issue), but from what research i’ve done it looks a little unlikely that it would be my issue?
either way, any help much appreciated!