Pressure jump on supersonic velocity inlet

Viktor

I have supersonic velocity inlet with two gases of different densities. Both gases have the same static pressure and velocity. First issue is that Fluent only stable with 1st order scheme. Second, on the inlet in the point separating two gases I have static pressure lower then prescribed. I tried prescribe total pressure and total temperature it blows up. What might be the reason and the way to avoid these problems. Thank you.