I have never used the exact material that you speak of, however we do miles of stainless RSW here every day.  One thing that comes to mind is the quenching effect after the material leaves the rolls.  Is this a dry weld, or a coolant flooded weld?  We have both applications, and the external coolant flooded process presents a whole host of problems.  Either way, feed speed, and pressure are the key to maintain quality welds.  The pressure is the most important factor because that truly dictates the resistance in the joint.  More pressure= more current to produce solid weld.  More current= more heat input.  More heat input= faster cooling rate, all of which can lead to weld cracking.  There is a file line between proper pressure and excessive pressure, and can only be optimized by performing a DOE of sorts starting at lower pressures and work your way up progressively.  Wheel size, and weld size requirements also need to be looked at as a potential problem if the wheels are too big/ small for the application.
Give us some more info, weld size requirements, transformer KVA, PSI force at the wheel interface (not air/ hydraulic cylinder PSI), feed rate, and any thing else that you have.
Mark