My first comment would be that you should probably try to solve this problem as a steady, incompressible flow. Assuming a 7kPa pressure drop across the system and applying Bernoulli’s equation comes out to about a 106 m/s flow (approximately 0.31Ma).
Given the relatively low Mach number, this flow will probably be very stiff to solve with a compressible solver. This somewhat shows up in your diverging convergence plots. Worst case scenario, back the flow speed down a little bit and get it solved in a fully incompressible region then move up to a compressible flow.