we had a similar problem on a multi port manifold and failed to sort it out. Keen to see what happens here. We ran the problem with very high mesh densities and it did not resolve the issue. It did make an initial improvement but it did not make it go away. If anything should be close it should be the mass conservation calc.
I think if you do not get balanced mass flow then it is time to double check the surfaces that you picked, units, ... geometry... surface goals not volume goals ... all goals average values as apposed to max or min...
a) For global goals include: Mass fluid, Mass flow rate, Static pressure.
b) Suppress the porous media and see if this resolves the issue.
Thanks everyone for the help. I created very fine local meshes at my outlets and I mostly eliminated the difference in mass flow and volume flow. I believe the averaged value was being reported as misleadingly low due to low resolution at those locations.