FWIW - I did have problems with G31 with the SmoothStepper. I think most/all of these problems were eventually resolved, but there were times when it would do just plain bizarre things - like moving opposite the commanded direction, moving the wrong axis, moving the wrong speed, even moving multiple axes. This cost me more than a few probes (I was using rigid probes). But, then, I seemed to be plagued with all kinds of problems that nobody else had. Happily, since switching to a KFLop, and my own custom CNC controller app, I haven't had one single problem of any kind, and the whole system has become dead reliable.
Regards,
Ray L.