CAPE-OPEN

before you can get a property from a material object (short of the properties that are available at phase equilibrium, which are flow rate, composition, pressure, temperature and phase fraction), you must first calculate the property using CalcSinglePhaseProp.

Note that CAPE-OPEN unit operations may not have side effects on material objects connected to feeds, so this CalcSinglePhaseProp may not be performed on the feed material object itself. But you can duplicate the feed material object, and perform the calculation on the temporary material object that results from that. Or copy the feed to the product first, then perform the calculation.

Turns out I overlooked this step indeed. Thanks as usual for great support and tips. Working as intended now.