I believe I'm one of those three you mention. In my case, the problem has been with the cart bottoming out on certain passages, even with perfectly flat records. I thought at first that the suspension on my cart was damaged and sent it back for a checkup. When it was returned, it exhibited the same problem so I sent it back a second time with explicit explanation of the problem. I just received it back from AJ and it is still exhibiting the same problem.
I am at a loss to understand what is happening - I have used different headshell plates with my Schroeder CB1 to vary the effective mass of the tonearm with little effect. I have played around with zenith, azimuth, anti-skate, VTF, and VTA. VTF and VTA can mitigate the problem but not solve it completely.
What's really odd is that for some reason, I can always get through the first track of any record without a hiccup - the issue happens starting with the second or third track so it seems position related. I rotated the tonearm mount thinking maybe my tonearm had an issue but it did not affect this particular condition. Also, at one time I was using my FR64s and it had the same problem - at the time I attributed this to the effective mass of that tonearm being beyond the prescribed 14-16g of the Master Sig.
Also, the way this thing behaves, is it seems to bottom out on dynamic passages - almost like there's some EMF kick-back on the coil that causes the motor to reverse - i.e. like the motor pushes on the cantilever. Hard to describe but here's a video showing what is happening.
If anyone has any thoughts on what might be going on here, I am open ears as I've exhausted my own troubleshooting skills.
In regards to patience - yes, I am being patient because when this cart plays, it's about as good as I've ever heard from my analog setup. I would even keep it just to play the first track of every album side I have if that's all I can get from it ;-)))