Check Valve Failure: Symptoms and Repair

In my passionate and, until now, unsuccessful search for the problem with the "intake manifold pressure control difference," I have now discovered that a small check valve in the vacuum system is defective. It allows flow in both directions. For those who are not familiar with it, it separates the pressure reservoir for the N75 valve at the turbocharger from the solenoid valve for the EGR system. Could it be that my problem arises because the error code is triggered under load, causing the car to go into limp mode?

I've checked everything that was suggested here and that I could check on my own. So, I've gone through everything except for using VAG Com to read data while driving.
So:
Values checked with VAG COM while stationary -> everything is as it should be.
VTG wastegate valve swapped with the AGR valve -> no change.
MAP sensor replaced in the engine control module (ECM) -> no change.
Looking for faulty hoses from the turbo to the intake manifold -> Found nothing.
VTG adjustment checked for smooth operation -> it's working well.
All vacuum system lines replaced -> no change, but a faulty check valve was found (has been ordered).

I'm afraid that's probably not it either, because there's nothing about it mentioned anywhere here.

Okay, could you please explain how the boost pressure behaves at full load?
too low, or too high, or excessively exaggerated.

It can also happen with turbos; if they get too hot, the variable turbine geometry (VTG) can get stuck.

I'll try to go for a drive in the coming days with a passenger who can operate the "Schleppi" (likely a specialized vehicle or equipment). And I'll also try to test all the "pressure routes" starting from the turbocharger.

"Unfortunately, the problem with the emergency mode is far from uncommon. I can get it into emergency mode in less than a minute, including starting the car, if I really push it. If I try to overtake someone, I can get past them, and then it immediately goes into emergency mode. The more load there is, the faster it happens. For example, on the highway, if I want to drive over 140 km/h, I can't go more than 300 meters without it immediately going into emergency mode. Even if I accelerate gently, it still happens, but it takes a little longer than when I'm almost at full throttle."

I'm not even sure how long this problem has been so severe, because I usually don't rev the engine above 2000 RPM, or at most 2100 RPM when I'm driving at 100 km/h. And it doesn't happen then. I don't think it's ever happened below 3000 RPM, but it definitely happens above that. The higher the RPM, the faster it occurs.