2018 STI boost dropping suddenly at high rpm after turbo upgrade

Hi i upgraded my stock turbo on my 2018 STI to tomei 7690 and ever since boost drops suddenly at around 6000 rpm. looking at logs(screen shot attached) nothing indicating why boost is dropping suddenly (not tapering down just drops suddenly) from 1.4 bar to 0.3 bar. The throttle stays @100%, wastegate duty stays at commanded duty cycle as in the wastegate duty cycle tables. i suspected the stock diverter valve is the issue even though i was running the stock turbo at same boost pressure and never had this issue. so i replaced the factory diverter valve to GFB mach2 and the same exact behavior i even installed a stiffer spring in the diverter valve but with no change. i installed the restrictor from the stock turbo in the new turbo wastegate line thinking maybe there is too much flow that the wastegate solenoid cant vent and making the wastegate opens and that made the turbo hit target boost better (no over/under shoot) but made the problem worse now boost is dropping @5300 rpm. i did almost everything and replaced everything i can think off that can cause this problem there are no leaks in the wastegate lines, the wastegate actuator, intercooler/couplers, diverter valve i dont know what could be the problem i hope you guys can help. note: i noticed the more wastegate duty cycle i add to raise boost i get more lag(100 to 200 rpms) to hit target i dont know if that is related to this issue.

mods list:

tomei 7690 turbo

255lph fuel pump

aem fuel regulator

FIC 1000cc injectors

torque solutions rails

replaced all engine bay fuel lines to -6

ETS top mount

GFB mach2 diverter valve

aem methanol injection kit

tuned using ECUtek software

Update: the issue is actually from the GFB diverter valve weak spring. last time I installed a stiffer spring and it didn’t solve the problem today I installed even stiffer spring and it solved the problem. I was afraid if I installed too stiff spring the valve won’t be able to open but I found out that it operated fine. I was able to hit 1.6 bar of boost up to redline @7400 rpm’s.