Stainless steel has higher resistance than Copper or Aluminum so at higher currents it starts to heat up. Its only a problem if high current passes through stainless steel, like washers or nuts in between the wire lug and the sensor pads(Ive seen this too often), but if its just used to fasten the lugs directly to the sensor pads then thats aok.
If you need to place washers and nuts in between the sensor pads and wire lug(to prevent squishing the PCB) then use nickel plated copper. Dont forget lock washers or loctite, you dont want loose nuts at those currents.
Thanks
Roy