Update:
Changed injectors to rx7 550cc and now still at 1.0bar its cutting earlier 6300rpm compared to 6700rpm with stock injectors.
Did another test, changed wastegate spring to 0.6bar and it cuts at 6900rpm. Increased the boost to 0.9 bar via avcr and it cuts at 6600rpm.
Cannot think of anything else but that this cut is related to boost somehow. When it occurs its very similar to the sound of rev cut and the car becomes very rich at that particular instant(11.6 to 10.1/10.2 approx). Car is very smooth until it gets to that point.