If you're using aftermarket pods then you should use an aftermarket machine too, nespresso puts the gasket required to build pressure on the pod itself, and this gasket is patented preventing aftermarket pods from having the same gasket design. Since the gasket is on the pod it is not on the machine meaning that stock nespresso machines will have issues with aftermarket pods. Some aftermarket machines have their own seal, which compensates for this problem when using aftermarket pods.
For more info see: https://www.youtube.com/watch?v=HouzvJGazs4