Okay found something interesting today while changing outside fresh air filters.
Both fresh air and back pressure flap are at 0%, but both are fully open.
Did readdress with ISTA+, still the same. Is this normal?
Thing is, for vent flap, it's the other way around, 100% for full open (at least that what I assumed when the air blowing from the vent at 100% value).

Still haven't gone to AC shop to check pressure.